This lets the default test time be 10 minutes when using a maximum
steps value. This will prevent the current 10 second limit from
kicking in and aborting. Also changes the --test-time override to
be more clearly a calibration time, and adds a new --test-time that
lets the user override the actual trial test time.

Bug: b/172480147
Change-Id: I630aa8d3c9e118bb5f0100b38f37e717e12f3538
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2523371Reviewed-by: Paul Thomson <paulthomson@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>