Enable HostsAdminTestXML
Enable HostsAdminTestXML

Although there is hosts_client class for XML, HostsAdminTestXML is
disabled. This patch enables HostsAdminTestXML.

Change-Id: Ib136661107a94f3e2c1607dad644dce0a3b42502
Closes-Bug: #1261968

JioCloud/tempest-lib,mtreinish/tempest-lib,cneill/tempest-lib,afaheem88/tempest-lib,sorenh/tempest-lib,varunarya10/tempest-lib