bozo: allow start of fs and dafs bnodes with options

bozo: allow start of fs and dafs bnodes with options

fs_create() and dafs_create() issue stat() to verify
the existence of each executable specified in the bnode.
However, commit fda2bc874751ca479365dc6389c0eebb41a0bda1
inadvertently removed the code that stripped any command
arguments before the stat().  Therefore, any bnode that
specifies arguments (e.g. /usr/afs/bin/dafileserver -d 5),
causes the stat() to fail and the bnode will not start.

Rename function AppendExecutableExtension() to a less
"window-ish" name: PathToExecutable().

Modify the Windows version of PathToExecutable()
to properly strip arguments.

Reimplement the Unix macro as function PathToExecutable()
that properly strips arguments.

Change-Id: I04f7ce2afb8211bd12b9063db1335738bff1cc1e
Reviewed-on: http://gerrit.openafs.org/11934
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>