Add doc and test for verbose parameter

We currently have support to show verbose output for image-list
with the command ``glance --verbose image-list`` but there is
no documentation about it.
This patch adds the documentation and a test to run it via CLI.

Closes-Bug: #1969565
Change-Id: Ic6db4f5ab2fecded373b044aa002f9a9bc262513

doc/source/cli/glance.rst

@@ -69,6 +69,10 @@ See available images::
 
     glance image-list
 
+To get a verbose output including more fields in the image list response::
+
+    glance --verbose image-list
+
 Create new image::
 
     glance image-create --name foo --disk-format=qcow2 \

glanceclient/tests/unit/v2/test_shell_v2.py

@@ -368,6 +368,12 @@ class ShellV2Test(testtools.TestCase):
                 {}, ['ID', 'Name', 'Disk_format', 'Container_format',
                      'Size', 'Status', 'Owner'])
 
+    def test_do_image_list_verbose_cmd(self):
+        self._run_command('--os-image-api-version 2 --verbose image-list')
+        utils.print_list.assert_called_once_with(
+            mock.ANY, ['ID', 'Name', 'Disk_format', 'Container_format',
+                       'Size', 'Status', 'Owner'])
+
     def test_do_image_list_with_include_stores_true(self):
         input = {
             'limit': None,