L3 agent should always use a unique CONF object

L3 agent should always use a unique CONF object

The l3 agent accepts an oslo configuration in its constructor and uses
it throughout the code, but there are some references to the global
configuration object held by the oslo library. Since HA functional
tests need to create two agents, the configuration should be consistent
throughout the code.

The important difference between the agents is their 'host' value so
that they create different namespaces, and 'state_path' value so the
agents get their own filesystem root.

Co-Authored-By: Assaf Muller <amuller@redhat.com>
Related-bug: #1374946
Change-Id: I3326889482681dd631ca59271ebd6a5d5129ae70