By default, the watch timer in Fluentd is set to True.
To save CPU and I/O consumption this can be set to False, which
kolla-ansible has been hardcoding so far.

When the watch timer is disabled, in_tail relies entirely
on inotify. In certain constellations, this may not work
reliably. In these cases, the watch timer needs to be activated, so this
change adds a variable to make the setting configurable.

Change-Id: Ic8ce6fbc3ed8f31d5d090e114b35703532679729