1. Replaces --crankshaft with --opt in tests.
2. Also fixes presubmit to check for --opt flag when
assertOptimized is used.
3. Updates testrunner/local/variants.py and 
v8_foozie.py to use --opt flag.
This would mean, nooptimize variant means there are
no optimizations. Not even with %OptimizeFunctionOnNextCall.

Bug:v8:6325

Change-Id: I638e743d0773a6729c6b9749e2ca1e2537f12ce6
Reviewed-on: https://chromium-review.googlesource.com/490206
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44985}