monitor: Add ignoring feedback sensors above allowed max

There may be situations where fan rotor feedback speeds above the
allowed range could be ignored, essentially ignoring any overspeed
detections. This adds an optional `ignore_above_max` attribute to the
fan sensors that can be added, set to 'true', to ignore marking that fan
sensor as nonfunctional when its above the allowed max. Without this
attribute, the fan sensor must remain within the allowed min/max range
to be deemed functional. This is the default behavior.

Change-Id: I4876b4c1963a8a1becd55732ca19496f5df6b003
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
6 files changed