Add environment variable to force keeping ANSI codes

If SOONG_UI_ANSI_OUTPUT is set to a true value force the simple status
output to keep ANSI codes.  This will allow buildbots to collect logs
with ANSI codes in them.  Smart status output is not affected as it
always keeps ANSI codes.

Bug: 147310922
Test: manual
Change-Id: I0b78ceebb65125b8e8dafb4787816fb679d3eb3e