Make MidoNet plugin code more testable

Refactor plugin.py and midonet_lib.py to improve unit testing of
the MidoNet plugin.  Make all the tests pass in the plugin except
those that test features that are not currently supported by the
plugin, which are IPv6 and multiple subnets per network.
Consolidate the mocking code in mock_lib.py to be shared by
plugin.py and midonet_lib.py.

Change-Id: Idcdfc3d90d5ec9e0be29bb6833d336af596fe363
Fixes: bug #1133215
Signed-off-by: Ryu Ishimoto <ryu@midokura.com>
Signed-off-by: Tomoe Sugihara <tomoe@midokura.com>
Fix typo

Change-Id: I83bdbd5d58a217d616bb2bb68f82ef6586d7b715
Imported Translations from Transifex

Change-Id: I9ad53953b1902c2538fe6888773ea0d7811371d3
Merge "Fix typo"
Merge "Make MidoNet plugin code more testable"
Merge "Imported Translations from Transifex"