The configuration of the DNS resolver is useful if the IPA server has
internal DNS support.

The installation of packages is happening before the DNS resolver is
configured, therefore package installation needs to be possible without
the configuration of the DNS resolver.

The DNS nameservers are configured for `NetworkManager`, `systemd-resolved`
(if installed and enabled) and `/etc/resolv.conf` if neither NetworkManager
nor systemd-resolved is used.

Example inventory:

  [ipaserver]
  ipaserver.example.com

  [ipaclients]
  ipaclient1.example.com

  [ipaclients:vars]
  ipaadmin_principal=admin
  ipaadmin_password=MySecretPassword123
  ipaclient_domain=example.com
  ipaclient_configure_dns_resolver=yes
  ipaclient_dns_servers=192.168.100.1
  ipaclient_cleanup_dns_resolver=yes

New parameters:

ipaclient_configure_dns_resolver
  The bool value defines if the DNS resolver is configured. before deploying
  the client. This is useful if the IPA server has internal DNS support.
  ipaclient_dns_server need to be set also.
ipaclient_dns_servers
  The list of DNS server IP addresses. This is only useful with
  ipaclient_configure_dns_resolver.
ipaclient_cleanup_dns_resolver
  The bool value defines if DNS resolvers that have been configured before
  with ipaclient_configure_dns_resolver will be cleaned up again.

New module:

roles/ipaclient/library/ipaclient_configure_dns_resolver.py

Fixes: #902 (Consider adding support for client DNS resolver
             configuration)