Fix docstring in method list_networks_on_dhcp_agent
Fix docstring in method list_networks_on_dhcp_agent

For function list_networks_on_dhcp_agent in the
python-neutronclient\neutronclient\v2_0\client.py,
the description is "Fetches a list of dhcp agents
hosting a network". However this function fetches
a list of networks hosted on a DHCP agent.

Change the docstring.

Change-Id: Ifa833d9a7ecab8ba55283d41d7a336d20cb578c3
Closes-Bug: 1802472

openstack/python-neutronclient,openstack/python-neutronclient,noironetworks/python-neutronclient,noironetworks/python-neutronclient