try harder when starting vdsmd

I've observed a situation when ha-agent is started too early and
it fails to start vdsmd, but later when vdsmd is started ha-agent
also starts fine. This patch makes agent to wait a while and retry
if the first attempt to start vdsmd fails

Change-Id: I806437b8c5eafd32fb37d0b3f2f59995faa28cdc
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>