core: Connect Storage Pool on iSCSI update

We should catch the exception when calling ConnectStorageServer
since we should try to connect all the hosts,
and if one of them fails we should keep try to connect all the other
hosts.

Change-Id: I4b125471920792d8bfaae2327e6aa757c378ef0e
Bug-Url: https://bugzilla.redhat.com/1102687
Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>