bitbake: cooker/server: Fix up 100% CPU usage at idle

The recent inotify changes are causing a 100% cpu usage issue in the
idle handlers. To avoid this, we update the idle functions to optionally
report a float value which is the delay before the function needs to be
called again. 1 second is fine for the inotify handler, in reality its
more like 0.1s due to the default idle function sleep.

This reverts performance regressions of 1.5 minutes on a kernel build
and ~5-6 minutes on a image from scratch.

(Bitbake rev: 0e0ba408c2dce14a0fabd3fdf61d8465a031495b)

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

bitbake/lib/bb/server/process.py

@@ -135,6 +135,9 @@ class ProcessServer(Process, BaseImplServer):
                     nextsleep = None
                 elif retval is True:
                     nextsleep = None
+                elif isinstance(retval, float):
+                    if (retval < nextsleep):
+                        nextsleep = retval
                 elif nextsleep is None:
                     continue
                 else: