Fix bug #8395 - optimize serverid_exists() for Solaris.

Fix bug #8395 - optimize serverid_exists() for Solaris.

jra asked:

    Do you have any idea on how many calls it saves,
    and what help the optimization gives ?

As far as calls: Not 100% sure, dtrace pointed the issue out to me, and when I
saw 10-50%(Or more), I looked for an easy fix.

The real expense here is the fnctl locks on the database.  That's pretty
painful.  1000ns per call, and probably 3-4 calls in that chain.  So it doesn't
take much to come out ahead was my math.
(cherry picked from commit 9bf2b3034b4c9523bfac779e518a2a1a6d76ef46)