firmware_builder: exclude on-device tests from code-coverage
firmware_builder: exclude on-device tests from code-coverage

When building host-based unit tests for code coverage, don't build
the on-device unit tests.

BUG=b:156895937
BRANCH=None
TEST=Run firmware_builder.py with --code-coverage option. Verify that
the 'test' command does not build unit tests for bloonchipper.

Signed-off-by: Paul Fagerburg <d8c44b60afb21c60f56d931aa690ca1cf34910c8@google.com>
Change-Id: I5e4f49b4911529a42b08fa7cd041dccff2c7513c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2702322
Commit-Queue: Paul Fagerburg <d8c44b60afb21c60f56d931aa690ca1cf34910c8@chromium.org>
Commit-Queue: LaMont Jones <01939f9990a33aa2509cfaed21d2f9ba201a2b37@chromium.org>
Tested-by: Paul Fagerburg <d8c44b60afb21c60f56d931aa690ca1cf34910c8@chromium.org>
Reviewed-by: Sean McAllister <ed4d2242d1138bb5c12488824add2e57e1144bd4@google.com>
Reviewed-by: LaMont Jones <01939f9990a33aa2509cfaed21d2f9ba201a2b37@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec