ansible_ipa_server.py

The common_check function in the replica installer code has been changed
for the new memory checker code. With this the server and replica command
line installers got the option --skip-mem-check.

The server and replica role now also support the memory cheker and there
are new variables for server and replica:

    ipaserver_mem_check - for ipaserver
    ipareplica_mem_check - for ipaserver

These bool values default to yes and can be turned off in the inventory
or playbook if needed.

Related to freeipa PR https://pagure.io/freeipa/issue/8404 (Detect and
fail if not enough memory is available for installation)

Fixes: #450 (IPA Replica Installation Fails)