Update treeherder-client from 1.7.0 to 2.0.1
Update treeherder-client from 1.7.0 to 2.0.1

It now requires mohawk/requests-hawk/six, and no longer requires oauth2
and httplib2. The sub-dependencies have been separated to make it easier
to spot orphaned dependencies in the future (treeherder-client isn't
used directly by try_extender, but via mozci).

adusca/try_extender,adusca/try_extender