libuafs: Allow -mountdir to override uafs_Setup

libuafs: Allow -mountdir to override uafs_Setup

For some reason, uafs_Setup accepts a parameter specifying the AFS mount
point, and we effectively ignore any -mountdir option specified in the
string arguments. Allow -mountdir to override the mount point specified
in uafs_Setup, by changing afs_mountDir &co during afsd_mount_afs().

Change-Id: I4ea88923c0a8392d280c1a8f0ca4d3adf741f7f6
Reviewed-on: http://gerrit.openafs.org/3897
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>