devtools: Rename cmdline.NewEnv to cmdline.EnvFromOS
devtools: Rename cmdline.NewEnv to cmdline.EnvFromOS

This is more descriptive, and matches test/modules.EnvFromOS.

Change-Id: I8227b36a51d169455b0e65172dc5814db59e11f6
MultiPart: 1/3

vanadium/go.jiri,vanadium/go.jiri