Change logic to use p4d init script only from /p4/N/bin.
The current logic sets a variable essentially preferring the p4d
init script in /etc/init.d, using the one in /p4/N/bin only if the
one in /etc/init.d doesn't exist as a file (and would not be
selected if it was a symlink).
* Referencing the file/symlink in /etc/init.d introduces
potentially complex and confusing behavior. If there were
a file in /etc/init.d rather than symlink'd, that could be
bad if it doesn't get upated with new versions of the SDP,
where stuff in /p4/N/bin should be reliably updated.
* I just expect the SDP to always use its own files in /p4/N/bin,
under direct control of the perforce user, rather than external
references to it. In a proper SDP deployment on Linux,
/etc/init.d should contain symlinks for SDP init scripts
anyway. But why trust that if there's no need?
* If there is a file in /etc/init.d and it's different than
/p4/N/bin for some reason, we should prefer the one in /p4/N/bin.
* The sylminks in /etc/init.d are outside the direct control of
the perforce user, and could point to who-knows-where.