scripts/unit-test: Support running tests only

By default we will still run all of the checks so that our CI coverage
is still sane. However, this will make it possible for developers to
trivially run just the test cases of the project for faster turnaround
time for developing. Just set TEST_ONLY=1 in your environment to skip
all of the slow checks like valgrind / coverage / clang-tidy.

Tested:
    Ran under an autotools build and meson build to verify that the
    behavior is still as expected.

Change-Id: I0b420e1c3e779863b90288ce72fc056400226734
Signed-off-by: William A. Kennington III <wak@google.com>
2 files changed