Fix mysql instance create failed when enable skip-name-resolve
Fix mysql instance create failed when enable skip-name-resolve

In the guestagent code, it create os_admin user only grant
privileges on host:localhost, but use host:127.0.0.1 to
connect to mysql. Modify host privileges grant on to 127.0.0.1
to avoid create instance failed when enable skip-name-resolve
in config file.

Change-Id: Ifa69461c8a55464f88aec001d067450eedccf172
Closes-bug: #1729225

zhangg/trove,openstack/trove,openstack/trove,zhangg/trove