bitbake: cooker: Improve pyinotify performance

bitbake: cooker: Improve pyinotify performance

Benchmarks show that the introduction of pyinotify regressed
performance. This patch ensures we only call the add_watch() function
for new entries, not ones we've already processed which does improve
performance as measured by "time bitbake -p".

This doesn't completely remove the overhead but it does substantially
reduce it.

(Bitbake rev: 493361f35f6cc332d4ea359a2695622c2c91a9c2)

(Bitbake rev: f668b347a8f9563f41d454288b9d4632190f308f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>