Allow -q to be repeated for very quiet output

Allow -q to be repeated for very quiet output

Even with the -q flag specified, tracing output is still mixed
with messages about signals and process exit status, which is
often irrelevant.  Allow the -q option to be repeated to force
the suppression of signals / exit status info too.

* defs.h: Change 'qflag' from 'bool' to 'unsigned int'.
* strace.1: Document ability to repeat '-q' option.
* strace.c: Allow '-q' to be repeated to quieten process
exit status and signal messages.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>