mount options can be lost when using bg option

When mounting an NFS export *without* the "bg" option, try_mount() is
called only once. Before calling it, the variables mount_opts and
extra_opts are set up. Then try_mount() calls nfsmount(), the latter
assumes that the aforementioned variables can be modified. Most
significantly, it allows the variable extra_opts to be modified.

When the "bg" mount option is used *and* the first try_mount() attempt
fails, it daemonizes the process and calls try_mount() again,
unfortunately, we've lost the required mount options in the variable
extra_opts.

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>