Add RST version of ganeti-watcher man page

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>

man/ganeti-watcher.rst

+ganeti-watcher(8) Ganeti | Version @GANETI_VERSION@
+===================================================
+
+Name
+----
+
+ganeti-watcher - Ganeti cluster watcher
+
+Synopsis
+--------
+
+**ganeti-watcher** [``--debug``]
+[``--job-age=``*age*]
+[``--ignore-pause``]
+
+DESCRIPTION
+-----------
+
+The **ganeti-watcher** is a periodically run script which is
+responsible for keeping the instances in the correct status. It has
+two separate functions, one for the master node and another one
+that runs on every node.
+
+If the watcher is disabled at cluster level (via the
+**gnt-cluster watcher pause** command), it will exit without doing
+anything. The cluster-level pause can be overriden via the
+``--ignore-pause`` option, for example if during a maintenance the
+watcher needs to be disabled in general, but the administrator
+wants to run it just once.
+
+The ``--debug`` option will increase the verbosity of the watcher
+and also activate logging to the standard error.
+
+Master operations
+~~~~~~~~~~~~~~~~~
+
+Its primary function is to try to keep running all instances which
+are marked as *up* in the configuration file, by trying to start
+them a limited number of times.
+
+Another function is to "repair" DRBD links by reactivating the
+block devices of instances which have secondaries on nodes that
+have been rebooted.
+
+The watcher will also archive old jobs (older than the age given
+via the ``--job-age`` option, which defaults to 6 hours), in order
+to keep the job queue manageable.
+
+Node operations
+~~~~~~~~~~~~~~~
+
+The watcher will restart any down daemons that are appropriate for
+the current node.
+
+In addition, it will execute any scripts which exist under the
+"watcher" directory in the Ganeti hooks directory
+(``@SYSCONFDIR@/ganeti/hooks``). This should be used for lightweight
+actions, like starting any extra daemons.
+
+If the cluster parameter ``maintain_node_health`` is enabled, then the
+watcher will also shutdown instances and DRBD devices if the node is
+declared as offline by known master candidates.
+
+The watcher does synchronous queries but will submit jobs for
+executing the changes. Due to locking, it could be that the jobs
+execute much later than the watcher submits them.
+
+FILES
+-----
+
+The command has a state file located at
+``@LOCALSTATEDIR@/lib/ganeti/watcher.data`` (only used on the master)
+and a log file at ``@LOCALSTATEDIR@/log/ganeti/watcher.log``. Removal
+of either file will not affect correct operation; the removal of the
+state file will just cause the restart counters for the instances to
+reset to zero.