Allow overriding environements on command line

Add a new command line option -e to override environement variables when
running a service.

Signed-off-by: Chmouel Boudjnah <chmouel@chmouel.com>
Merge pull request #529 from chmouel/override-environement

Allow overriding environements on command line
TLS support, with same env vars as docker client

Thanks to @jkingyens for the bulk of the work.

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>