use register_cli_opts instead of register_opts

oslo.config provides api register_cli_opts
to register multiple opts at once and same
is used in this patch to replace the
register_opts

Change-Id: I80b9bf37308c9e7085947200bc7c393c15e5e29d
Closes-bug: #1336224
Use None instead of mutables in method params defaults

Mutables in the method params defaults might cause errors and
that's why it's anti-pattern in most of the cases and should be
removed.

Change-Id: I8bc284f12ce72082a0482410ec2c20c2fc087a4b
Closes-Bug: #1327473
UnitTests: fix mock assertions usage

Some unit tests used mock.Mock().assert_called_once() assertion.

This is wrong as the mock.Mock object has no such interface method,
so due to mock nature such wrong assertion do essentially nothing
and always pass.

Change-Id: I9ed5ba26aa099c362644a4f09d67a2f9bf36f382
Closes-Bug: #1336766
Merge "Use None instead of mutables in method params defaults"
Merge "UnitTests: fix mock assertions usage"
Merge "use register_cli_opts instead of register_opts"