Fix the log prefix for runzeo.py.

The file used to be called runsvr, but was changed.  Change the label
to RUNZEO to match the name of the file.

Add the process ID to distinguish different processes when tests are
running.

src/ZEO/runzeo.py

@@ -286,9 +286,14 @@ def debug(msg):
     """Log a debugging message."""
     _log(msg, zLOG.DEBUG)
 
+# XXX It would be nice if a program that extended this one (like
+# runzrs) could change the label.
+
+_label = "RUNZEO:%d" % os.getpid()
+
 def _log(msg, severity=zLOG.INFO, error=None):
     """Internal: generic logging function."""
-    zLOG.LOG("RUNSVR", severity, msg, "", error)
+    zLOG.LOG(_label, severity, msg, "", error)
 
 
 # Main program