Ansible TRANSFORM_INVALID_GROUP_CHARS deprecation warning because of dash in group names

[pmeulen]

Ansible 2.8 shows a deprecation warning because we use group names with a dash ("-").

Output when running deploy in verbose mode:

Not replacing invalid character(s) "set([u'-'])" in group name (stepup-app)
[DEPRECATION WARNING]: The TRANSFORM_INVALID_GROUP_CHARS settings is set to allow bad characters in group names by default, this will change, but still be user configurable on deprecation. This feature
 will be removed in version 2.10. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.
 [WARNING]: Invalid characters were found in group names but not replaced, use -vvvv to see details

Not replacing invalid character(s) "set([u'-'])" in group name (stepup-app)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-gateway)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-gateway)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-gateway)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-middleware)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-middleware)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-middleware)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-ra)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-ra)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-ra)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-selfservice)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-selfservice)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-selfservice)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-tiqr)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-tiqr)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-tiqr)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-keyserver)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-keyserver)
Not replacing invalid character(s) "set([u'-'])" in group name (stepup-keyserver)