4578: utils.is_playbook support fqcn import_playbook

[OscarBell]

Updated utils.is_playbook function to support the fqcn version of import_playbook to detect a valid playbook file.

[OscarBell]

This PR will solve issue: #4578

[OscarBell]

Alternatively if the playbooks_keys needs to be unadjusted we could change below line
if not isinstance(item, Mapping) or not playbooks_keys.intersection( item.keys() ):
into
if not isinstance(item, Mapping) or not playbooks_keys.intersection( {item.split('.')[-1] for item in item.keys()} ):
With above solution all keys found in the play will be changed into the non-fqcn variant and can be compared against the playbook_keys