Added option to redirect stdout on run_command_always.

There are cases where a command should not write to stdout. For example,
when sending the initial broadcast before the header is printed.

This change adds this option to run_command_always, and uses enums to
make it easier to read what's been passed to it.

BUG: 27953643

Change-Id: I9aed0cb0df4112b31d2079241114e206b9d0bb0c