Fix _validate_mac_address method

The method _validate_mac_address previously used: netaddr.EUI(data)
which would convert data passed in to the correct mac_address representation.
For example if data=123 it would return: EUI('00-00-00-00-00-7B'). To fix
this issue I used netaddr.valid_mac() instead which returns a bool if a mac is
valid or not and does not raise. Note this file needs some improvements to
improve how exception handling is done that will come later.

Change-Id: I4fb868e40abbad9e743028cc768f47ca9b3e0e70
Closes-bug: 1291163
Fix wrong section name "security_group" in sample config files

The section name [security_group] in Sample config files of
ML2 and Big Switch plugins was wrong and it should be
[securitygroup].

Change-Id: I8204b2f37f96a5e46038e117853ac8637a9705fd
Closes-Bug: #1304105
BigSwitch: Stop HTTP patch before overriding

Stops the default HTTPConnection patch used by the
Big Switch tests before patching HTTPConnection with
another substitution. This prevents mock from losing
track of the default patch which was resulting in it
not consistently being stopped by the stopall call in
cleanup.

This also corrects an incorrectly targeted mock for the
HTTP patch in one of the test files.

Closes-Bug: #1303605
Change-Id: Ia5b374c5f8d3a7905d915de4f1f8d4f3a6f0e58d
Merge "Fix _validate_mac_address method"
Merge "BigSwitch: Stop HTTP patch before overriding"