netinfo: bootproto4 is now 'dhcp'/'none' instead of a boolean

testSetupNetworksAddDelDhcp verifies the new property.

Legacy BOOTPROTO parameter is set in a network's or iface's
['cfg'] dictionary to mimic information from ifcfg files
which may be missing in current setups.

Change-Id: Iaef31f93da978a5793fceae28763ceafedb8d3b6
Bug-Url: https://bugzilla.redhat.com/987813
Signed-off-by: Ondřej Svoboda <osvoboda@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/25170
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>