When interactive is true, check_call is used instead of check_output,
and check_call doesn't return the command output.

Bug: 1074357
Change-Id: Ib9e761d41d754df58c9ee1f897dde173ce4d9eff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2170805Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>