Use standard assertVolumeStatusWait for volume detachment

Custom volume state detection method in test_compute_with_volumes
is unreasonable for volume detachment. Because in contrast to
volume attachment the target volume state ('available') is set when
all detachment processes have been finished.

Change-Id: I6d3d1186e73175fb25e2204088866cf53f61f4d5
Related-Bug: #1355285
diff --git a/tempest/thirdparty/boto/test_ec2_instance_run.py b/tempest/thirdparty/boto/test_ec2_instance_run.py
index f3f11fd..00b17d9 100644
--- a/tempest/thirdparty/boto/test_ec2_instance_run.py
+++ b/tempest/thirdparty/boto/test_ec2_instance_run.py
@@ -306,8 +306,7 @@
 
         volume.detach()
 
-        self.assertVolumeStatusWait(_volume_state, "available")
-        wait.re_search_wait(_volume_state, "available")
+        self.assertVolumeStatusWait(volume, "available")
 
         wait.state_wait(_part_state, 'DECREASE')