Git does not have access to regular environment variables when cloning

[BYK]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?

Git fails to connect to repos behind a proxy since certain environment variables are not passed to it when making the call. Internal reference: t19705486.

If the current behavior is a bug, please provide the steps to reproduce.

Block git access without a proxy and then try to use the proxy. Normal git xxx commands from the shell passes but commands issued by yarn fails.

What is the expected behavior?

yarn commands to behave like the ones executed from the shell.

Please mention your node.js, yarn and operating system version.

Node v6.10.3
yarn 0.27.1