Add automated test involving video capture hardware

This is a nascent attempt to write some automated tests to ensure that
stb-tester continues to work with all our current supported hardware.  It's
currently very basic but works.  The intention is that in the future we
will have a test rig such that all commits are tested with real hardware
to prevent future regressions.

The test is currently very basic, it just checks to see if something major
goes wrong but in the future we can add greater control over the input
to the hardware (e.g. using a Raspberry Pi) to measure other properties
such as quality, latency, startup/shutdown time, ability to recover from
video loss, ability to handle HDMI renegotiation, etc.
Hardware tests: Add test_blackmagic_intensitypro
Rename tests/{hardware-test => hardware}

For consistency with tests/ocr
Move all utility functions from tests/{run-tests.sh => utils.sh}

This keeps all the utility functions used by the self-tests in a single
place.
tests/run-tests.sh: Test suites passed on command line must be relative to caller

...not relative to `run-tests.sh`. This will allow me to move the
hardware-specific test suite into tests/hardware/ in a future commit (so
that it doesn't get run by default).

This changes the command-line API of run-tests.sh but that is a change
that only affects developers, not users, of stb-tester.
Run hardware tests with `make check-hardware`

Instead of `STBT_ENABLE_HARDWARE_TESTS make check-integrationtests`. I
feel that a separate `make` target is better documentation than having
to read the source code of test-hardware.sh. Also, this allows us to run
the hardware tests separately (for example only after the non-hardware
tests have passed).

To exclude the test cases in `tests/test-hardware.sh` from `make
check-integrationtests` I had to move `test-hardware.sh` out of
`tests/`, into `tests/hardware`.

One consequence of this change is that `tests/test-install` (the
temporary installation used to run the tests) isn't removed after `make
check` completes. It's already in `.gitignore`.
test_teradek_vidiu: Avoid infinite loop if crtmpserver fails to start

Wait for up to 10 seconds instead.
Merge pull request #128 from wmanley/hardware-test

Add automated test involving video capture hardware