Preliminary time-sync and usage support

Optionally enable STv2 event playback through the
time_sync service and early UsageHandler support.

Change-Id: I5988d320fe41df29c52ebdb8e579bf0d7f53a45f
tox verification and tarball venv packaging support.

Optionally run tox on each git repo (-t) and package resultant
venv into a tarball on success (-p)

tarball filename includes the short-sha1 of the repo.

If tarball is created, screen is not run.

Change-Id: I1f0e533aad017033810eb3c9f132ab9e5855d809