As the old way to include tasks is deprecated, replace static include
statements with import_tasks and dynamic ones with include_tasks.
Increaded the required ansible version to 2.5.0 to make sure that
include_tasks and import_tasks is working as expected.
Fixes issue #38
The support for external cert files is not complete yet.
Please have a look at the example inventory file inventory/hosts.replica and
also the install and uninstall playbook files install-replica.yml and
uninstall-replica.yml