Test fx subcommands

Command Description
run-host-tests DEPRECATED! build and run tests on host
self-test run tests of fx and subcommands
test Entry point for all Fuchsia tests (host, target and end-to-end)
testgen Component integration test auto-generator
core-tests run zircon core-tests
coverage Runs test and exports coverage data.
run-e2e-tests run e2e tests
smoke-test Finds and runs tests affected by the current change.
test-rustdoc runs "fx rustdoc" on all rust targets
test-stats Query and calculate test stats.
test-stats.py Query and calculate test stats.