Open syscall emulation file O_RDONLY

Open syscall emulation file O_RDONLY

As reported on the -info mailing list, docker is now exporting the
/proc filesystem as read only.  ioctl() doesn't need write permissions
to do its work, so change O_RDWR to O_RDONLY.

Reviewed-on: http://gerrit.openafs.org/12122
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 359e1f2a25d242984229edfb378c0b95c3ee8570)

Change-Id: I5ec9262a30c1aa40604e1265b4da00f4597c1cc8
Reviewed-on: http://gerrit.openafs.org/12124
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>