iproute2, netinfo: Change the location of our dhclient lease files

To prepare for DHCPv6 support, name the files 'dhclient[46]-iface.leases.
The plural not only mirrors the 'generate_lease_file_name' function
in initscripts but also reflects the fact that there is usually more
than one lease in the files.
DHCPv4 lease files now carry a '4' in the name for simplicity, explicitly
suggesting the DHCP flavour used.

Also simplify globs representing our and 3rd party lease files locations.

Change-Id: I0eb2d3c7b8163684f3bb8c59ad908a260d2138b6
Signed-off-by: Ondřej Svoboda <osvoboda@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31111
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>