api-ref: add 'compressed' container_format

The 'compressed' container format was added by change I62159315346e
in Train, but apparently we forgot to update the api-ref.

Change-Id: I4f46e7c25606fd6da34aaaada5e40cc2e27915a6

api-ref/source/v2/images-parameters-descriptions.inc

@@ -14,7 +14,10 @@
     |p-start|\ The format of the disk.\ |p-end|
     |p-start|\ Values may vary based on the configuration available in a
     particular OpenStack cloud. See the :ref:`Image Schema <image-schema>`
-    response from the cloud itself for the valid values available.\ |p-end|
+    response from the cloud itself for the valid values available.  See
+    `Disk Format
+    <https://docs.openstack.org/glance/latest/user/formats.html#disk-format>`__
+    in the Glance documentation for more information.\ |p-end|
     |p-start|\ Example formats are: ``ami``, ``ari``, ``aki``, ``vhd``,
     ``vhdx``, ``vmdk``, ``raw``, ``qcow2``, ``vdi``, ``ploop`` or
     ``iso``.\ |p-end|
@@ -29,7 +32,13 @@
     |p-start|\ Format of the image container.\ |p-end|
     |p-start|\ Values may vary based on the configuration available in a
     particular OpenStack cloud. See the :ref:`Image Schema <image-schema>`
-    response from the cloud itself for the valid values available.\ |p-end|
+    response from the cloud itself for the valid values available.  See
+    `Container Format
+    <https://docs.openstack.org/glance/latest/user/formats.html#container-format>`__
+    in the Glance documentation for more information.\ |p-end|
     |p-start|\ Example formats are: ``ami``, ``ari``, ``aki``, ``bare``,
-    ``ovf``, ``ova``, or ``docker``.\ |p-end|
+    ``ovf``, ``ova``, ``docker``, or ``compressed``.\ |p-end|
     |p-start|\ The value might be ``null`` (JSON null data type).\ |p-end|
+    |p-start|\
+    **Train changes**: The ``compressed`` container format is a supported
+    value.\ |p-end|

api-ref/source/v2/samples/schemas-image-show-response.json

@@ -42,7 +42,8 @@
                 "bare",
                 "ovf",
                 "ova",
-                "docker"
+                "docker",
+                "compressed"
             ],
             "type": [
                 "null",

api-ref/source/v2/samples/schemas-images-list-response.json

@@ -63,7 +63,8 @@
                             "bare",
                             "ovf",
                             "ova",
-                            "docker"
+                            "docker",
+                            "compressed"
                         ],
                         "type": [
                             "null",