Migrated subunit-trace.py from tempest

This migrates the above files from tempest. This includes tempest
commits:

ecaa61e Merge "Fail tempest if 0 tests are run"
118dfea Merge "Remove test start output in pretty tracer"
8ce8acb Fail tempest if 0 tests are run
8a81d2e Remove test start output in pretty tracer
b38f2f1 Merge "Correct misspelled words"
a4c086b Correct misspelled words
5541db7 Merge "Add total runtime to summary output"
8dfc88e Add total runtime to summary output
7357907 Merge "Change how tempest debug logs are displayed"
b3ca686 Change how tempest debug logs are displayed
813793c Merge "create test and worker summary report"
31ad041 create test and worker summary report
05fa8b5 Merge "Add in a concurrency aware subunit filter"
063bcb8 Add in a concurrency aware subunit filter
bc68916 Add README

to see the commit history for these files refer to the above sha1s in
the tempest repository

Change-Id: Ided295ec08c57bc64e0f96307df9e233febd886a