Send master start/stop events
Send master start/stop events

Buildbot Makefile now invokes send_monitoring_event when 'start' and 'stop'
are run.

BUG=470916

Review URL: https://codereview.chromium.org/1004353005

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@294592 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build