OpenPower: Return unavailable if any error in deleting host dump

If there is a failure in sending dump delete request to host
for resource and system dump, return unavailable error.

Signed-off-by: Dhruvaraj Subhashchandran <dhruvaraj@in.ibm.com>
Change-Id: Ia85ef46c55c5a2b54af2b8632f94c3318ef1d4d1