vol: use OS_DIRSEP in many more places

vol: use OS_DIRSEP in many more places

For consistency use OS_DIRSEP and OS_DIRSEPC throughout the
package.

(cherry picked from commit 259a0e886a29874420010544e33a789cac1692c1)
Reviewed-on: http://gerrit.openafs.org/3702
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Change-Id: Id18bbe7759bc96f83c7a00a0a8698a868fc54c2a
Reviewed-on: http://gerrit.openafs.org/3900
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>