Add basic timing instrumentation to devtest.sh

Adding basic instrumentation to devtest to gain an understanding of
the time used for each step, and the impact of adding elements such
as pip-cache. Also allows comparison of runtime for different network
environments.

Change-Id: Id99b8c47ec34f16dab54e8f8534f00d5d638fedc
Merge "Add basic timing instrumentation to devtest.sh"