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: I20744e4957fbd5b039fdd52ac530f11ac6d72319
partially-implements: blueprint testcase-description
b5603bc4f8