Making docker build work behind http proxy

As some of us are working behind corporate firewalls
and some of us are not the docker build and execution
should work in both proxy and non proxy environemnt.
This chnage adds this support.

Note: npm gives a warning when no proxy is used. I could not
figure out any good way to work this around. Any comments are welcome.

Change-Id: Ic9afb1c83fbe33fd2c78d913d3c7c8e10200a2b4
Signed-off-by: Gergely Csatari <gergely.csatari@nokia.com>