Log configuration values for OFA agent

When other agents start up, they log the configuration values
to their logs. This patch adds the same feature to the
Openflow agent.

fixes bug 1289139

Change-Id: Ibab20154805a12ec265a2499cbfd6c376c376130
Use a temp dir for CONF.state_path

external_pids will defaults to $state_path(/var/lib/neutron)/external/pids
which isn't accessible when running unit tests so use a tempdir for
CONF.state_path. This bug arose when oslo.config 1.3.0 came out which
fixed bug #1282250 (I4324bda6f3de3cdf05f8eb3cf16052c04018dec8) and
caused this issue.

Change-Id: I253c5ea85c51eff94399da0b9462d10a9c509a0f
Closes-Bug: #1301027
Merge "Log configuration values for OFA agent"