Fix tempest case "test_delete_ss_from_sn_used_by_share_server"

The case use fake data in security service, which may cause backend driver
fail.
Refer to the case "test_try_update_valid_keys_sh_server_exists", just ignore
the error of the backend driver procedure.

Change-Id: I783652486fcf92b543c0a620409c9e41d33cab56
Closes-Bug: #1531758
1 file changed
tree: 816086d81f16bc21d8a93c933624592ad236848c
  1. manila_tempest_tests/