Changes

testenv: pass env var for --binary-repo

Pass TESTENV_BINARY_REPO=1 to the podman container if the --binary-repo
argument is set. This will be used for the BTS testsuite to figure out
from where we need to run fake-trx.

Change-Id: Ia88906147e2e579145e3c8d04090c58f533febd5

bts/run_fake_trx.sh: tweak cd logic

Don't test if FAKE_TRX_DIR is empty, because it is never empty at that
point. If it was empty, then the line above would assign a default
value.

Change-Id: I63f9720487b564de5c5609eb52a6bb9d5a8aa74f