Stop mock patches by default in base test class

Adds a mock.patch.stopall to the base unit test
case cleanup routines to stop patches by default
in unit tests. This behavior can be overwritten
by setting an attribute on the test class if
required.

Also removes the explicit stops in the Cisco n1kv,
VMware, and NEC unit tests to leverage the new
automatic cleanup.

Closes-Bug: #1290550
Change-Id: Ic642430a765ea8deb07ebd88b619da58a58e0edd
Merge "Stop mock patches by default in base test class"