client: flag in cachemanager if rmtsys is enabled

when processing "fs sysname" on a client, a rmtsys-related
checks are executed by default. These prevent a user with gid
2750 and 274i8 (0xabc and 0xabe) from executing this command.
Add a new flag inside the cachemanager for the rmtsys-
functionality. This flag is set through a new ioctl by the afsd
on startup.

Change-Id: Idf95aa81cc1dbb46c70a11b9ae2ccfa04bfb4c4f
Reviewed-on: http://gerrit.openafs.org/10245
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>