When global_environment_variables is set in user_variables.yml, this
installs environment settings in /etc/environment on all hosts and
containers. These remain in place after deployment is complete.
This patch adds a similar variable deployment_environment_variables
that defines environment strings applied only while the playbooks
are running. They leave nothing behind on the hosts or containers.
This may be used, for example, for proxy settings required only
during deployment. A simpler no_proxy setting is adequate during
deployment, so this provides a workaround to Bug #1691749.
Change-Id: Ia15d2133c6749fa9496bbf9359b8bf075742d60e
Related-Bug: #1691749
77ac88197c