libafs: Consolidate afs_DaemonOp code

libafs: Consolidate afs_DaemonOp code

Create the AFS_DAEMONOP_ENV define to simplify the logic of when we
perform afs_DaemonOp-y code paths. Also create the daemonOp_common
function, to perform common pre-fork operations that are common
between platforms.

Change-Id: Id93e1ffd7b8f4c0029cf4632239a519a619e9f9f
Reviewed-on: http://gerrit.openafs.org/4188
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>