Add test for whitespace behavior in env flags.
Add test for whitespace behavior in env flags.

rust-lang/cargo,nipunn1313/cargo,eminence/cargo,eminence/cargo,rustyhorde/cargo,tshepang/cargo,rustyhorde/cargo,eminence/cargo,tshepang/cargo,rust-lang/cargo,nipunn1313/cargo,tshepang/cargo,rustyhorde/cargo,rust-lang/cargo,rust-lang/cargo,eminence/cargo,nipunn1313/cargo,rustyhorde/cargo,tshepang/cargo,nipunn1313/cargo