Port service to Python 3
Port service to Python 3

Fix ProcessLauncher._pipe_watcher() on Python 3. On Python 3,
eventlet.greenio.GreenPipe.read() requires a length parameter. Reading
one byte is enough to be notified when the parent dies unexpectedly.

Fix _is_daemon() on Python 3: catch io.UnsupportedOperation before
catching OSError because io.UnsupportedOperation now inherits from
OSError in Python 3. By the way, the comment was wrong: the io module
exists in Python 2.6.

Remove whitelist of tests working Python 3 from tox.ini since all tests
now pass on Python 3.

Change-Id: Iba8b35e535cd0d869f87f5b790243cf9c0728de8

openstack/oslo.service,eezhova/oslo.service,citrix-openstack-build/oslo.service,poznyakandrey/oslo.service