Modified Script to Parse Time from Arguments
Modified Script to Parse Time from Arguments

Example usage:
`./long_term_health.py --from-date=2016-10-1 --to-date=2017-11-2`
The tool would now need to fetch all the chrome version released between 1st October, 2016 to 2nd of November 2017.

You may also do the following:
`./long_term_health.py --from-date=2016-09-23 --to-date=68`
In this case, it would download the version released after the 23rd of September, 2016 to version 68.

The following will also be valid:
`./long_term_health.py --from-milestone=50 --to-date=2018.7.1`
This will download the version 50 to all the versions released before 1st of July, 2018.

The default behavior is to run the latest *10* milestones against the latest benchmark.
`./long_term_health.py`

Bug: chromium:863390
Change-Id: I0b6d89c1e7d9706b7b970a5c39ed52a506281959
Reviewed-on: https://chromium-review.googlesource.com/1145317
Commit-Queue: Leonard Ge <a985a80ed457409fab3d693f0de5252e07c70d59@google.com>
Reviewed-by: Juan Antonio Navarro Pérez <1649bb5e6b9eafe026580e338065dc64ba6b80b2@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult