Add API Error Handler (#74)

* Add error handler that converts from rpc.Status errors to Watchtower API errors.

* Better testing for ErrorHandler.

* Rename testcase and remove empty default switch case.

* Change the error status back to int64.

* Converting everything to int32s.

jsonpb wraps int64s as a string which we dont like.  We'll figure out how to use values larger than int64s when it comes up.

* Remove special casing for TraceId which isn't needed anymore.

* Removing wrappers from error details since we never need to know when they are set or unset from the end user.

* Using the helper error functions inside the project service.

* Correct usage of hclog, replace panic with Error log.

* Adding periods to all API returned errors, correct spelling, fix missed invalid argument error not using helper function.

* Change our logged errors to Error instead of Warn.

* Add TODO for defining and using our own defined API error codes.

* Add TODO to remove internal error messages.

internal/proto/local/controller/api/v1/error.proto

@@ -4,22 +4,20 @@ package controller.api.v1;
 
 option go_package = "github.com/hashicorp/watchtower/internal/gen/controller/api;api";
 
-import "google/protobuf/wrappers.proto";
-
 message ErrorDetails {
-	google.protobuf.StringValue trace_id = 1 [json_name="TraceId"];
-	google.protobuf.StringValue request_id = 2 [json_name="request_id"];
+	string TraceId = 1 [json_name="TraceId"];
+	string request_id = 2 [json_name="request_id"];
 	repeated string request_fields = 3 [json_name="request_fields"];
 }
 
 // Error is returned by the JSON API when an error occurs.
 message Error {
 	// The HTTP Status code applicable to this error
-	google.protobuf.Int64Value status = 1;
+	int32 status = 1;
 	// An application-specific error string
-	google.protobuf.StringValue code = 2;
+	string code = 2;
 	// A human readable explanation specific to this occurrence of the error
-	google.protobuf.StringValue message = 3;
+	string message = 3;
 	// Additional metadata regarding the error. Depending on the error
 	// different fields will be populated.
 	ErrorDetails details = 4;