setup logger name of NeutronCommand automatically

It is a common pattern to add
class XXXCommand(NeutronCommand):
    log = logging.getLogger(__name__ + '.<command name>').
So introduce a metaclass to do that automatically in order to simplify
the code a bit.

Closes-Bug: #1258028
Change-Id: I7908e3e2c0f3f04d9e57360f6ba22e153d0d35bd
Merge "setup logger name of NeutronCommand automatically"