This was omitted when these tests were added.
Adding this means that the tests now see the `$DOCKER_HOST` configured (via
`$TEST_DOCKER_HOST`) where they didn't before. In some cases (specifically the
`test-e2e-connhelper-ssh` case) this results in additional output on stderr
when `-D` (debug) is used:
time="2019-04-03T11:10:27Z" level=debug msg="commandconn: starting ssh with [-l penguin 172.20.0.2 -- docker system dial-stdio]"
Address this by switching the affected test cases to use `-l info` instead of
`-D`, they all just require some option not specifically `-D`. Note that `info`
is the default log level so this is effectively a nop (which is good).
Signed-off-by: Ian Campbell <ijc@docker.com>