zmake: allow running coverage reports for a single test
zmake: allow running coverage reports for a single test

When trying to increase the code coverage it is common to verify the
new test's effect by wanting to re-run the coverage report. Update
zmake to allow doing so for a single test.

BRANCH=none
BUG=none
TEST=zmake -D configure --test --coverage zephyr/test/drivers
     Check that build/zephyr/test/drivers/output/zephyr.info exists
     and is valid

Signed-off-by: Yuval Peress <50dc11c009bd4d7e9d9d15a383c1743ce5ee82ef@google.com>
Change-Id: Ie0a716b6e0fabbbcd5a5e7c6bbec3a8470578cd5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3195198
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Reviewed-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>

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