ci: jobs.sh: Introduce a quiet version of run_cmd

ci: jobs.sh: Introduce a quiet version of run_cmd

We've started using the run_cmd helper function to log what kind of
command is being executed as well as actually executing the command.
The problem however is doing I/O redirections for commands which we
don't wish to see any output for whatever reason. Now, if the
redirection is applied at parameter passing to run_cmd it's going to be
applied to the debug print as well. Let's introduce another helper,
run_cmd_quiet which takes care of the I/O redirection and executes the
command completely silently.

Signed-off-by: Erik Skultety <eskultet@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>