Correctly create the dhcp_agent.ini and l3_agent.ini

The section [ovs] is needed only for ovs/ovn configurations.

TrivialFix

Change-Id: If9015b8f53c04cf3257331449ebd50163fabcab0
Signed-off-by: Maksim Malchuk <maksim.malchuk@gmail.com>
(cherry picked from commit 78260f98)