Add support for a --run-test-option to testrunner.

Sometimes it is useful to send specific run-test options to every
test. This adds a --run-test-option argument to testrunner that will
let one pass any run-test options down to run-test with no
modification.

Test: ./test/testrunner/testrunner.py \
        --host \
        --run-test-option='--with-agent libtifast.so=log,MethodEntry,MethodExit' \
        -t 001-HelloWorld

Change-Id: Ice8e5b83fce4389b7461f5284c093dd144969640