run_command() was using the undefined variable 'cmd', rather than the
pass in parameter 'command'.

Bug: angleproject:5210
Change-Id: I5e80869b18b717835217ad14a562bb4d223d52c4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2765005Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>