Adding description for testcases - compute part10

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: I0ca6cbed5b2f8517096ed95e40c5e5766862c012
partially-implements: blueprint testcase-description
9 files changed