See #10141 for more info, but the main point of this is to make sure
that if you do "docker run -e FOO ..." that FOO from the current env
is passed into the container. This means that if there's a value, its
set. But it also means that if FOO isn't set then it should be unset in
the container too - even if it has to remove it from the env. So,
unset HOSTNAME
docker run -e HOSTNAME busybox env
should _NOT_ show HOSTNAME in the list at all
Closes#10141
Signed-off-by: Doug Davis <dug@us.ibm.com>
642218cefa
