Description of problem:
I can create duplicate ansible variables of the same name for the same role.
These duplicates can be of different types

Duplicates shouldn't be allowed similarly to puppet classes

Version-Release number of selected component (if applicable):
Satellite-6.6.0 Snap14

How reproducible:
deterministic

Steps to Reproduce:
1. Import ansible roles: 
# hammer ansible roles import --proxy-id 1

2. Create ansible variable "my_var" assigned to "theforeman.foreman_scap_client" role:
# hammer ansible variables create --variable my_var --variable-type string --ansible-role theforeman.foreman_scap_client
Ansible variable [my_var] was created.

3. Try to create variable of the same name once again:
# hammer ansible variables create --variable my_var --variable-type boolean --ansible-role theforeman.foreman_scap_client
Ansible variable [my_var] was created.


Actual results:
# hammer ansible variables list --search name=my_var
---|----------|---------------|---------|-------------------------------
ID | VARIABLE | DEFAULT VALUE | TYPE    | ROLE                          
---|----------|---------------|---------|-------------------------------
28 | my_var   |               | boolean | theforeman.foreman_scap_client
27 | my_var   |               | string  | theforeman.foreman_scap_client
---|----------|---------------|---------|-------------------------------

>>> duplicate vars for one role are allowed

Expected results:
2nd "my_var" creation fails with something like
"Validation failed: my_var for the role already exists"