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.

Reviewed-on: http://gerrit.openafs.org/4188
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 6143bb27d20380e689346b4e66c077e5d4cd6061)

Change-Id: I8878b5b55871c1974b19c2af64636ea536841bff
Reviewed-on: http://gerrit.openafs.org/5777
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>