Fix uniqueness bug with dicts using keys other than name

[ejseqera]

Found with adding members, the result from find_name() returned none because the --name key does not exist.

Resolved with defining keys to check membership for in items with strings or lists. Test with:

members:
   - user: '[email protected]'
     organization: '$TOWER_ORG_NAME'
     overwrite: True
   - user: '[email protected]'
     organization: '$TOWER_ORG_NAME'
     overwrite: True

Where dryrun returns:

DEBUG:root:DRYRUN: Running command tw members add --user [email protected] --organization $TOWER_ORG_NAME
DEBUG:root:DRYRUN: Running command tw members add --user [email protected] --organization $TOWER_ORG_NAME