try harder when connecting the storage

the agent has to wait between attempts to connect the storage
to give vdsm some time to initialize

Change-Id: I4c512aad490366b0fbd890d156b37243993dc498
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1119702
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>