tools/xc: handle tty output differently in stdiostream_progress

tools/xc: handle tty output differently in stdiostream_progress

If the output goes to a tty, rewind the cursor and print everything in a
single line as it was done up to now. If the output goes to a file or
pipe print a newline after each progress output. This will fix logging
of progress messages from xc_save to xend.log.

To support XTL_STDIOSTREAM_SHOW_PID or XTL_STDIOSTREAM_SHOW_DATE print
the output via vmessage if the output is not a tty.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>