Change the default hardcoded values of the dnsmasq dns resolvers
on dhcp_agent.ini.j2 to a configuration option part
of group_vars/all.yml.
Also adding 1.1.1.1 as part of the default set.
Change-Id: I629c69e556d4ddba19f68f06627038e1886ae5f9
Signed-off-by: Jorge Niedbalski <jorge.niedbalski@linaro.org>