make ipmid respond to SIGTERM and SIGINT for clean shutdown

On some systems ipmid was not responding to SIGTERM so systemd
could not shut it down in a clean manner, resorting to SIGKILL
after a long timeout. This adds code to respond to SIGTERM and
SIGINT and safely unwind all the provider libraries on exit.

Tested-by: running ipmid; in another shell, and running
           'killall -15 ipmid' or 'killall -2 ipmid' to send
           SIGTERM or SIGINT and watch that ipmid shuts down
           in a controlled and timely manner.

Change-Id: I690846796523bebea1a08845c0d17e1df2a94fee
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
2 files changed