OpenPOWER: Clear system and resource dump entries while powering off

The dumps like system and resource dumps are stored in host memory
and that will be lost during a power off, so the entries in BMC
dump-manager for those dumps will be stale after a power off.
This commit adds a service to call deleteAll to clear the entries
for system and resource dumps during system power off.

Tests:
   1 - Created a resource dump and system dump
       and activated the service
       Result: Both dump entries are cleared

   2 - Created a resource dump and system dump
       powered off the system
       Result: Both dump entries are cleared

Signed-off-by: Dhruvaraj Subhashchandran <dhruvaraj@in.ibm.com>
Change-Id: I4e6a59ae852c86f5edbab767fb6a0ff2a4635289