Add '-E' for grep

Maybe it is because merging conflict leads to the omission
of the patch:
https://review.openstack.org/#/c/558767/

Change-Id: I3f81787fc583187d95217b1a97b2dc64f3c182a1

zun/container/docker/host.py

@@ -78,7 +78,7 @@ class Host(object):
                     try:
                         cmd = "mount |grep $(df " + CONF.docker.docker_data_root + \
                               " |awk 'FNR==2 {print $1}') | grep 'xfs'" \
-                              " |grep 'pquota|prjquota'"
+                              " |grep -E 'pquota|prjquota'"
                         utils.execute(cmd, shell=True)
                     except exception.CommandError:
                         sp_disk_quota = False