bitbake: lib/bb: Fix string concatination potential performance issues

Python scales badly when concatinating strings in loops. Most of these
references aren't problematic but at least one (in data.py) is probably
a performance issue as the issue is compounded as strings become large.

The way to handle this in python is to create lists which don't reconstruct
all the objects when appending to them. We may as well fix all the references
since it stops them being copy/pasted into something problematic in the future.

This patch was based on issues highligthted by a report from AWS Codeguru.

(Bitbake rev: d654139a833127b16274dca0ccbbab7e3bb33ed0)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/process.py

@@ -326,10 +326,10 @@ class ProcessServer():
                         if e.errno != errno.ENOENT:
                             raise
 
-                msg = "Delaying shutdown due to active processes which appear to be holding bitbake.lock"
+                msg = ["Delaying shutdown due to active processes which appear to be holding bitbake.lock"]
                 if procs:
-                    msg += ":\n%s" % str(procs.decode("utf-8"))
-                serverlog(msg)
+                    msg.append(":\n%s" % str(procs.decode("utf-8")))
+                serverlog("".join(msg))
 
     def idle_commands(self, delay, fds=None):
         nextsleep = delay