add trace_requests option to debug section

this supports the use case that David Kranz has in tracing
specific tests for test development. Because this is expected to
be development only, and not used in a general case, we don't do
all the md5 niceties of the previous code.

Change-Id: Ia9c7a7d10456d0583f8897111b958050c8e95ed7
Merge "add trace_requests option to debug section"
Merge branch 'master' of https://github.com/openstack/tempest