nfs-utils: NFSv4: fix backgrounding

he nfsmount() function checks if !bg before running
switch(rpc_createerr.cf_stat). On the other hand, the nfs4mount()
function does not, and results in exiting the loop on the first
iteration even with the bg mount option.

NOTE: This and the previous patch ("nfs-utils: mount options can be lost
when using bg option") are relevant to non text-based mount options.

See https://bugzilla.redhat.com/show_bug.cgi?id=529370 for details.

Signed-off-by: Harshula Jayasuriya <harshula@redhat.com>
Signed-off-by: Steve Dickson <steved@redhat.com>