add wait code after the call of fuction subprocess_closefds.

Now in ovirt-node, we has the fail possible to get the output
the call of subprocess_closefds, because of not waiting for
the complete of the command.
This patch is to avoid the problem.

Change-Id: I3b5a7c41c5e6809d148bda37f3fb1a75ed3fd4dd
Signed-off-by: boh.ricky <boh.ricky@gmail.com>