Changing the queued element sent to the Solver to allow different
types of solver tasks to allow solving for cluster creation or
addition of services or any other type of cluster operation that
requires solver interaction. As part of this, renaming
ClusterRequest to ClusterCreateRequest.
Merge remote-tracking branch 'origin/develop' into feature/add-different-types-of-solve-tasks

Conflicts:
	server/src/main/java/com/continuuity/loom/codec/json/JsonSerde.java
	server/src/test/java/com/continuuity/loom/http/LoomClusterHandlerTest.java
renaming a field for clarity and using a more detailed error msg.
Merge pull request #69 from continuuity/feature/add-different-types-of-solve-tasks

Changing the queued element sent to the Solver to allow different