ovs-ctl: let openvswitch startup to NOT hold up system boot upon error

ovs-ctl: let openvswitch startup to NOT hold up system boot upon error

Abort openvswitch startup script if ovsdb startup fails for
some reason. This helps in getting the system startup to NOT hang
indefinitely, as was seen in a recent report when ovsdb failed with
"I/O error: /etc/openvswitch/conf.db: failed to lock lockfile
(Resource temporarily unavailable)" and system remained in hung state
forever, unless manually rebooted from console.

Signed-off-by: Sabyasachi Sengupta <sabyasachi.sengupta@alcatel-lucent.com>
[blp@nicira.com changed an 'if' statement to '||']
Signed-off-by: Ben Pfaff <blp@nicira.com>