Increase the maximum possible execution time to 120 seconds and add a new
command line flag `-t` which allows overwriting the default value.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
This prevents timing out ubus call when the child invokes further detached
childs inheriting stdio descriptors.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>