Revert Command dispose changes

The disposing of command objects is necessary to avoid the mediator
being used after it is disposed in cases where a MasterRefresh or
FLExBridge related shutdown and reopen of FLEx are performed.

Fix the dispose failures in the tests by actually disposing of the
Commands in the test code.

Change-Id: Ie2803a58e35163468b04d05cc7ea9f42fc0a2d9c