Validate dscp value less that 64

Previously neutron would raise a 500 error if the dscp value was greater
than 63. This patch adds validation to neutron so that a clear error
message is returned if the value is greater than 63.

Fixes bug 1200026

Change-Id: I41a93661952669d112463608be907eede1901490
Be compatible with oslo.config 1.2.0a3+

The private API of oslo.config changed, and the Cisco
options parsing code was using it.
Use an explicit MultiConfigParser instance for parsing
the config files.

Fixes LP Bug #1196084

Change-Id: I7ffcac3c295491fe9ba8abc7e98f33157a48c51b
Merge "Validate dscp value less that 64"
Merge "Be compatible with oslo.config 1.2.0a3+"