test-with-docker: add --env option to pass through env variables
test-with-docker: add --env option to pass through env variables

Adds simple mechanism to pass environment variables into
test-with-docker, which is occasionally useful, especially for
development and tinkering with tests. It's typically the right thing to
codify the environment variables into tests, but a pass through can be
handy.

The implementation is simple enough, passing the
variables into the docker containers.

Change-Id: I03c2feda8edc2983e423f862ed210fabb845714f
Reviewed-on: http://gerrit.cloudera.org:8080/11730
Reviewed-by: Laszlo Gaal <57b770caf3b7d570ebf40813dac2ce5f53722fa7@cloudera.com>
Reviewed-by: Joe McDonnell <2f04924382c6a21f96a9a4f8cbedc35ff4599584@cloudera.com>
Tested-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala