annotate stages of script

because the script is mostly not running under xtrace, we should
mark the script a little more so people can see when we are at
various phases.

Change-Id: I2e9e12dba4d2b14e3eea78d83d54360fc63e1f4f
calculate remaining timeout locally

instead of making assumptions on how much time to set aside for
the timeout, instead calculate the timeout for the main gate_hook
to be DEVSTACK_GATE_TIMEOUT - time elapsed when we enter the hook
- 5 minutes (to handle cleanup and upload time).

This will hopefully make accidental overage of the timeouts less
frequent occurrence.

Change-Id: I364f9c9926488699dc77dd49189d529607858316
Merge "annotate stages of script"
Merge "calculate remaining timeout locally"