stack delete fails when instance is soft deleted

In an environment where reclaim_instance_interval is set to
non-zero in nova, an delete request will only soft delete an
instance.(status=SOFT_DELETED, so that the instance can be reclaimed
if required by using 'nova restore <instance_id>')

Now in the above environment, when an delete stack is requested by
user, stack will hang until reclaim_instance_inerval or timeout.
Hence status=SOFT_DELETED for an instance should be handled by heat, which
this patch proposes.

Closes-Bug: #1377290

Change-Id: I86ea788131f113e3deb7aebfccecd7f5e4957ae5
Merge "stack delete fails when instance is soft deleted"