Enable tach signal handler

Register and handle tach change signals for each tach sensor.
Inventory would be updated when all tach sensors for a specific fan
enclosure have a tach value of zero.

Change-Id: Idd3f53c29c68c6171d858e616fbfe868f30a4ea9
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
4 files changed