Cleanup in keepalived tests

Cleanup in keepalived tests

A recent patch introduced a new keepalived manager utility
function which returns the keepalived.conf file contents,
but the keepalived functional test was not updated to use it.
Also, a bunch of unneeded logging configuration was removed from
this test.

Additionally, the keepalived configuration functional test
in the L3 agent testing module compares expected configuration
to an in-memory representation of the configuration that will
be persisted to disk. It's better to compare the expected
configuation with what was actually written to disk.

Change-Id: I0d6f73c5326d2ba1960456a151a67517db5cce7a