tests/drv_hangman: Add subtest for error state capture/dump

tests/drv_hangman: Add subtest for error state capture/dump

Guarantees that error capture works at a very basic level.

v2: Also check that the ring object contains a reloc with MI_BB_START
for the presumed batch object's address.

v3: Chris review comments:
 - Move variables to local scope.
 - Do not assume there is only one request.
 - Some gen encode flags into the BB start address.
 Also, use igt_set/get_stop_rings as suggested by Mika Kuoppala.

v4: Make as a subtest of drv_hangman.
v5: Rebase

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com> <v4>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>