Adding description for testcases - identity part5

When Tempest is used in customer site, often we are required to
provide a testcase list including testcase names and descriptions.
Now no this kind of doc is available, so we can add descriptions
with the format of doc string for every testcase, so later we
can generata such a testcase description list.

There are hundreds of testcases missing descriptions, so we can
add them gradually, and limit the modified files in one patch
for the convenience of reviewing.

Change-Id: I47fc64ac84b4d0ea3da0a9469efec7bd6e0b0f3d
partially-implements: blueprint testcase-description
9 files changed