test: allow options for v8 testing
Checklist
make test passes
Affected core subsystem(s)
v8
Description of change
Allow extra options when testing v8 in Node tree (see https://github.com/nodejs/build/issues/199 for more details). The extra options can be set by setting them in 8_EXTRA_TEST_OPTIONS.
I've found this is needed while investigating https://github.com/nodejs/node/issues/5263 will be generally useful. In particular for the CI job I want to use progress=dots instead of the more verbose default output