Fix status message inside validate_can_perform_action()
Fix status message inside validate_can_perform_action()

If we assign status with just self.db_info.task_status, we would get a
exception message like :
ERROR: Instance d6f3861d-21d2-4e96-9df1-64cf6439ea9c is not currently
available for an action to be performed (task status was (84 ERROR Build
error: guestagent timeout.)). (HTTP 422)

But here we actually need action only.

Change-Id: Iab69ba01937aa8e7a9be9e95e499d64891beed03
Signed-off-by: Fan Zhang <c5ad88d84fbb94b43047dfb6304f0dda87b1e69d@outlook.com>

openstack/trove,openstack/trove