OVS: update status according to admin_state_up

Fixes bug 1099099

In addition to this the code does the following:
1. validates if the port exists on the OVS when a port update event takes
   place
2. when a port is created the initial state is set as 'DOWN'. this is
   later updated by the agent when it is detected as up

Change-Id: I917d4b5aa8df7395fcaa841d77083546478739d2
Fix InvalidContentType can't be raised because of error in constructor

InvalidContentType exception class is defined two times:
in quantum.openstack.common.exception and quantum.common.exceptions
with two different signatures.
A lot of code like wsgi.Serializer.serialize() imports one of them but
attempts to use it with the signature of another one, which ends with
TypeError exception.

This change fixes the bug by removing the second definition of
InvalidContentType class and leaving only one which works correctly
with all code. Also adds unit tests for exceptions to prevent this and similar bugs.

Change-Id: I5d932d75ad184a0a6c6419190f2940bd47b7504e
Fixes: bug #1104090
Ensure that correct root helper is used

Fixes bug 1105193

Change-Id: Iaaf0b3687c410f5dbfa152d601ae3b2492a610dd
Merge "Fix InvalidContentType can't be raised because of error in constructor"
Reqd. core_plugin for plugin agents & show cfg opts loaded.

For the linuxbridge, openvswitch, nec, and ryu plugin agents,
require the core_plugin configuration option, and throw an
exception, if not present. Note: cannot make this a required
option for all agents, as there are agent that include the
core config options, but do not require core_plugin.

In addition, log (as debug) the configuration options that
have been loaded at start-up for these four agents. This will
help with diagnosing start-up issues related to the
configuraiton settings (or lack of).

Tested that exception thrown, when missing core_plugin
value in config file(s) included, for these four agents.

bug 1059923
Change-Id: I813f0c2a3d0ec01be74a34e56ab085979197a16a
Merge "Ensure that correct root helper is used"
Merge "OVS: update status according to admin_state_up"
Merge "Reqd. core_plugin for plugin agents & show cfg opts loaded."
Revert "Reqd. core_plugin for plugin agents & show cfg opts loaded."

This reverts commit 06ce1329a044b8e7be9db59811d4f4316d0d0743.

bug 1059923

patch was found to not be a valid fix.

Change-Id: I465974f60fd65b4d2c9449267ab108fac13d70c8