unit-test: fix and use CODE_SCAN_DIR

There are two different patterns for doing the equivalent of
    os.path.join(WORKSPACE, UNIT_TEST_PKG)

Convert them all to use the CODE_SCAN_DIR variable and set CODE_SCAN_DIR
using `os.path.join`.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I1f2386f105dae100176247c40092a93c35974422
1 file changed