Fix test framework to detect proper server PID

Previously the PID format was:
[PID] Timestamp

But it recently changed to:
PID:X Timestamp

The tcl testing framework was grabbing the PID from \[\d+\], but
that's not valid anymore.

Now we grab the pid from "PID: <PID>" in the part of Redis startup
output to the right of the ASCII logo.

tests/support/server.tcl

@@ -236,7 +236,7 @@ proc start_server {options {code undefined}} {
     
     # find out the pid
     while {![info exists pid]} {
-        regexp {\[(\d+)\]} [exec cat $stdout] _ pid
+        regexp {PID:\s(\d+)} [exec cat $stdout] _ pid
         after 100
     }