Carries the proxy variable while installing trove-integration

Closes-Bug: 1362797

Carries the proxy variable (http_proxy/https_proxy) to sudo,
while installing trove-integration.

"redstack install" fails to complete behind proxy as few of the installation
steps like "pip install" and "apt-get install" are processed under sudo
environment which does not carry the proxy variables exported in the local
environment.

Fix involves passing $HTTP_PROXY along with above mentioned installation
commands.

Change-Id: I23c0b5a5f6ae6cecacf15fc68be8e53effd03532