Remove skip from test_invalid_host_for_migration().

This commit removes the skip related to a bug, it was fixed as
part of grizzly-3, so we no longer to to skip the test because
of the bug.

Change-Id: I3ee2dab1e92732ad7a9fe5319b35524d7c2aff75
diff --git a/tempest/tests/compute/test_live_block_migration.py b/tempest/tests/compute/test_live_block_migration.py
index f2ec753..abaaf85 100644
--- a/tempest/tests/compute/test_live_block_migration.py
+++ b/tempest/tests/compute/test_live_block_migration.py
@@ -108,7 +108,6 @@
         self.servers_client.wait_for_server_status(server_id, 'ACTIVE')
         self.assertEquals(target_host, self._get_host_for_server(server_id))
 
-    @testtools.skip('Until bug 1051881 is dealt with.')
     @testtools.skipIf(not live_migration_available,
                       'Block Live migration not available')
     def test_invalid_host_for_migration(self):