the --timeout command line option is a custom feature added in some
linux distributions (fedora). Passing that command line argument will
make dhclient fail if the binary does not support it, preventing
activation of dhcp based connections.
Worse, the option has just been recently changed from "-timeout", so
that we are currently incompatibile with Centos, RedHat and older
versions of Fedora too.

Leverage the "timeout" option in dhclient config file: it will produce
the expected behavior and will be universally supported.

Fixes test: dhcp-timeout
Fixes: fa467360

https://bugzilla.redhat.com/show_bug.cgi?id=1491243