Support Optional Super User in Instance Create

The creation of initial users and/or databases is supported in an
instance-create request, but the creation of a super/root user is
not. Granted, it's possible to create or reset the root user, but it
must be done as a separate request, after the instance has completely
initialized.

Changeset: If CONF.root_on_create == True, a UUID is generated for
the root user's password and is returned in the instance-create
response as the "password" property/field.

Change-Id: I300d3f019766445b90411d5ab8651b1aa34a77e9
Implements: blueprint instance-initial-super-user
Closes-Bug: #1219624
Extract generic part of GA code from MySQL specific modules

Extract common part of MySqlAppStatus to superclass
in order to provide easier implementation of
other DB engines support

Blueprint: refactor-ga-for-other-engines-support

Change-Id: Id101cccb0181055153ad817c12b1056e989b598d
Merge "Support Optional Super User in Instance Create"
Merge "Extract generic part of GA code from MySQL specific modules"
Task manager refactoring done

Manager API class removed and rpc fake impl used now for integration
testing

Change-Id: If20004f1b69e41e8243a3f58eec184f1f457affe
Implements: blueprit trove-task-manager-client-refactoring