When stdout is redirected to some file or command two things will
happen:
- qvm-run will not automatically color the output as stdout is not a
TTY
- even when coloring is forced, it will not work, as the control
sequence (on stdout) will be redirected anyway
Fix this by handling stdout and stderr independently and output color
switching sequence to each of them.
FixesQubesOS/qubes-issues#2190