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 \