Skip test_volume_backed_live_migration()

This test has been flaky in the neutron multi-node jobs,
both non-DVR and DVR. Let's skip it for now so we can
make progress with live migration work.

Change-Id: I02a147008d5b926a6ad12ffcd4f7dbc308cf6ac7
Related-bug: #1549511
diff --git a/tempest/api/compute/admin/test_live_migration.py b/tempest/api/compute/admin/test_live_migration.py
index 3ad9305..b1c42a6 100644
--- a/tempest/api/compute/admin/test_live_migration.py
+++ b/tempest/api/compute/admin/test_live_migration.py
@@ -19,6 +19,7 @@
 from tempest.api.compute import base
 from tempest.common import waiters
 from tempest import config
+from tempest.lib import decorators
 from tempest import test
 
 CONF = config.CONF
@@ -129,6 +130,8 @@
     def test_live_block_migration_paused(self):
         self._test_live_migration(state='PAUSED')
 
+    @decorators.skip_because(bug="1549511",
+                             condition=CONF.service_available.neutron)
     @test.idempotent_id('5071cf17-3004-4257-ae61-73a84e28badd')
     @test.services('volume')
     def test_volume_backed_live_migration(self):