Add command line `--job-results-dir` to the Avocado runner, so we can
store the job results in a different directory than the one
configured.

Remove `--logdir` from the main avocado application,
this option is obsolete and actually it was not working.

Update the manual page regarding this change.
Signed-off-by: NRudá Moura <rmoura@redhat.com>