Remove status* fields from HealthMonitor model

Remove status* fields from HealthMonitor model

Status and status_description fields of HealthMonitor
model are never changed during lifetime of the object
and doesn't represent the status of it's pysical
implementation. Instead, status and status_description
of PoolMonitorAssociation is used. Another reason for
removing those fields is that HealthMonitor acts as
template which is instantiated on device. Status field
for template makes no sense.

fixes bug 1207650

Change-Id: Iea9d7f73c3a2db43c553ed06a64fe5ff42427167