fuse: Add -oallow_other by default where possible

By default, fuse mountpoints are only accessible by the same uid as
that which mounted the fuse filesystem. When we're running as root,
specify -oallow_other so by default anyone can access the afs
mountpoint.

Reviewed-on: http://gerrit.openafs.org/6390
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 83d3084e95ac025660f0b8064f49400eb94bfb60)

Change-Id: I4c2217bc18502d8b761645f38522c02fc91c4084
Reviewed-on: http://gerrit.openafs.org/9452
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>