Pass --runtime-option from testrunner to run-test.

Note that the python argument parser does not like option
arguments starting with a '-' if passed like
  --runtime-option -Xjitthreshold:0
so such options need to be passed with '=' as in
  --runtime-option=-Xjitthreshold:0

Test: testrunner.py --help (manual inspection)
Test: testrunner.py --host --jit -t 667-jit-jni-stub (OK)
Test: testrunner.py --host --jit -t 667-jit-jni-stub \
      --runtime-option=-Xjitthreshold:0 (2 FAILURES)
Bug: 62611253
Change-Id: I6ebe18fe27b24989320ad963516146d12da4664f