Mark the Sheepdog driver unsupported

The Sheep dog test runs have not been passing
in the gate for quite sometime, to the point the
tests were moved to the experimental queue.

The most recent failures show that Sheepdog is not
supported on Bionic and mailing list posts show it
as no longer being maintained [1].  Given all
these datapoints it is time to more it
unsupported.

[1] http://lists.wpkg.org/pipermail/sheepdog/2019-March/068449.html

Change-Id: Id7bcacaaf41b3cc9657c78de26111c0996df8775

cinder/volume/drivers/sheepdog.py

@@ -454,6 +454,10 @@ class SheepdogDriver(driver.VolumeDriver):
     # ThirdPartySystems wiki page
     CI_WIKI_NAME = "Cinder_Jenkins"
 
+    # TODO(jsbryant) Remove this driver in the 'U' release as it is no
+    # longer maintained.
+    SUPPORTED = False
+
     def __init__(self, *args, **kwargs):
         super(SheepdogDriver, self).__init__(*args, **kwargs)
         self.configuration.append_config_values(sheepdog_opts)

doc/source/reference/support-matrix.ini

@@ -253,7 +253,7 @@ driver.pure=complete
 driver.qnap=complete
 driver.quobyte=complete
 driver.rbd=complete
-driver.sheepdog=complete
+driver.sheepdog=missing
 driver.storpool=complete
 driver.synology=complete
 driver.tintri=missing

releasenotes/notes/sheepdog-mark-unsupported-648b2458d4a198de.yaml

@@ -0,0 +1,14 @@
+---
+upgrade:
+  - |
+    The Sheepdog driver has been marked as unsupported
+    and is now deprecated. ``enable_unsupported_driver`` will
+    need to be set to ``True`` in the driver's section in
+    cinder.conf to continue to use the driver.
+deprecations:
+  - |
+    The Sheepdog driver has been marked as unsupported
+    and is now deprecated. ``enable_unsupported_driver`` will
+    need to be set to ``True`` in the driver's section in
+    cinder.conf to continue to use the driver. The driver
+    is scheduled for removal in the 'U' release.