storage: add an helper method to disconnect the storage server
storage: add an helper method to disconnect the storage server

Add an helper method to HAClient to disconnect the hosted-engine
storage server.

Change-Id: Ib595116ed922ab081486bcea2c9052e823c50f2c
Related-To: https://gerrit.ovirt.org/48834/
Bug-Url: https://bugzilla.redhat.com/1001181
Signed-off-by: Simone Tiraboschi <cb03129c66ba4da7ba7044049d0f43907bf857bb@redhat.com>

oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha