From net references and my own testing, it looks like there is a bug in how Foreman-installer is handling the dhcpd.conf setup for dns-search.
It should be setting
option domain-search "mydomain.dick.jane.com","dick.net","jane.com"
in the /etc/dhcp/dhcpd.conf.
Instead the foreman-installer is setting it as:
option domain-search "mydomain.dick.jane.com,dick.net,jane.com"
which causes the dhcpclient process to throw an error and ignore these settings.
Here is a brief version of the foreman-installer run where I try to set the dns-search.
Foreman Installer Run to set
foreman-installer --foreman-proxy-dhcp-search-domains "mydomain.dick.jane.com","dick.net","jane.com" --verbose
...
Running installer with args [["--foreman-proxy-dhcp-search-domains", "mydomain.dick.jane.com,dick.net,jane.com", "--verbose"]]
...
[ WARN 2018-07-02 12:34:51 verbose]
/Stage[main]/Dhcp/Concat[/etc/dhcp/dhcpd.conf]/File[/etc/dhcp/dhcpd.conf]/content:
...
[ WARN 2018-07-02 12:34:51 verbose] + option domain-search "mydomain.dick.jane.com,dick.net,jane.com";
/etc/dhcp/dhcpd.conf
…
option domain-search "cbs.ad.cbs.net,cbs.net,cbs.com";
…
When I set the following in dhcpd.conf manually and restart dhcpd the client gets set correctly as shown in /var/log/messages
Jul 2 12:53:15 tlistmrsnd32 NetworkManager[824]: <info> [1530550395.7266] dhcp4 (eno16777984): domain name 'mydomain.dick.jane.net'
Jul 2 12:53:15 tlistmrsnd32 NetworkManager[824]: <info> [1530550395.7266] dhcp (eno16777984): domain search 'mydomain.dick.jane.net'
Jul 2 12:53:15 tlistmrsnd32 NetworkManager[824]: <info> [1530550395.7266] dhcp (eno16777984): domain search 'dick.net.'
Jul 2 12:53:15 tlistmrsnd32 NetworkManager[824]: <info> [1530550395.7266] dhcp (eno16777984): domain search 'jane.com.'
/etc/dhcp/dhcpd.conf modified outside of Foreman
...
option domain-search "mydomain.dick.jane.com","dick.net","dick.com";
...
Resolv.conf on client
# Generated by NetworkManager
search mydomain.dick.jane.com dick.net jane.com
nameserver 1.2.3.4
nameserver 5.6.7.8