Initial cut of wwapi.

We need an API for Warewulf in order to automate around it. The initial version of the API will look a lot like wwctl. wwctl will call the API so that we do not need to maintain separate code paths. In this preview wwctl calls the API via direct function call, but we can change that to a gprc or REST call to a Warewulf server in the future.

This commit contains:
wwapid WareWulf API Daemon. A grpc server with mTLS auth.
wwapic WareWulf API Client. A grpc client with mTLS auth. It's just a sample that reads the version from the server.
wwapird WareWulf API Rest Daemon. A http REST reverse proxy to wwapid.
There are also sample insecure and secure curls to test with.

Implemented Functionality:
wwctl node add
wwctl node delete
wwctl node list
wwctl node set
wwctl node status
wwctl container build
wwctl container delete
wwctl container import
wwctl container list
wwctl container show

Some notes on the files:

    Logic that was in wwctl has moved to warewulf/internal/pkg/api. wwctl just calls the API. wwctl functionality is unchanged.
    Everything under the /google directory is copied google proto code to stand up wwapird. It's a bit strange to copy in the code, but that is currently how it's done.
    Everything in warewulf/internal/pkg/api/routes/wwapiv1 is generated code.

There are some loose ends here, such as no service installers. I just ran off the command line for development.
The Makefile could use improvement. I'm building by make clean setup proto all build wwapid wwapic wwapird ; echo $?
I copied the configs from warewulf/etc to /usr/local/etc/warewulf manually.

google/api/client.proto

@@ -0,0 +1,99 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package google.api;
+
+import "google/protobuf/descriptor.proto";
+
+option go_package = "google.golang.org/genproto/googleapis/api/annotations;annotations";
+option java_multiple_files = true;
+option java_outer_classname = "ClientProto";
+option java_package = "com.google.api";
+option objc_class_prefix = "GAPI";
+
+extend google.protobuf.MethodOptions {
+  // A definition of a client library method signature.
+  //
+  // In client libraries, each proto RPC corresponds to one or more methods
+  // which the end user is able to call, and calls the underlying RPC.
+  // Normally, this method receives a single argument (a struct or instance
+  // corresponding to the RPC request object). Defining this field will
+  // add one or more overloads providing flattened or simpler method signatures
+  // in some languages.
+  //
+  // The fields on the method signature are provided as a comma-separated
+  // string.
+  //
+  // For example, the proto RPC and annotation:
+  //
+  //   rpc CreateSubscription(CreateSubscriptionRequest)
+  //       returns (Subscription) {
+  //     option (google.api.method_signature) = "name,topic";
+  //   }
+  //
+  // Would add the following Java overload (in addition to the method accepting
+  // the request object):
+  //
+  //   public final Subscription createSubscription(String name, String topic)
+  //
+  // The following backwards-compatibility guidelines apply:
+  //
+  //   * Adding this annotation to an unannotated method is backwards
+  //     compatible.
+  //   * Adding this annotation to a method which already has existing
+  //     method signature annotations is backwards compatible if and only if
+  //     the new method signature annotation is last in the sequence.
+  //   * Modifying or removing an existing method signature annotation is
+  //     a breaking change.
+  //   * Re-ordering existing method signature annotations is a breaking
+  //     change.
+  repeated string method_signature = 1051;
+}
+
+extend google.protobuf.ServiceOptions {
+  // The hostname for this service.
+  // This should be specified with no prefix or protocol.
+  //
+  // Example:
+  //
+  //   service Foo {
+  //     option (google.api.default_host) = "foo.googleapi.com";
+  //     ...
+  //   }
+  string default_host = 1049;
+
+  // OAuth scopes needed for the client.
+  //
+  // Example:
+  //
+  //   service Foo {
+  //     option (google.api.oauth_scopes) = \
+  //       "https://www.googleapis.com/auth/cloud-platform";
+  //     ...
+  //   }
+  //
+  // If there is more than one scope, use a comma-separated string:
+  //
+  // Example:
+  //
+  //   service Foo {
+  //     option (google.api.oauth_scopes) = \
+  //       "https://www.googleapis.com/auth/cloud-platform,"
+  //       "https://www.googleapis.com/auth/monitoring";
+  //     ...
+  //   }
+  string oauth_scopes = 1050;
+}