[BUG] Add a test to ensure that using PATCH API to update Roles Mappings works on a static role

[cwperks]

With the recent refactor of the security REST APIs introduced in #3123 a regression was made that changed the behavior of how the PATCH API to update roles mappings worked.

Before the PR was merged the PATCH API was able to perform operations on static roles.

> curl -XPATCH https://admin:admin@localhost:9200/_plugins/_security/api/rolesmapping/all_access --insecure -H "Content-Type: application/json" --data '
[
        {
        "op": "remove",
        "path": "/users",
        "users": ["jwt_test"]
        }
]
'
{"status":"OK","message":"'all_access' updated."}

After the PR was merged the PATCH API started failing with the following error:

> curl -XPATCH https://admin:admin@localhost:9200/_plugins/_security/api/rolesmapping/all_access --insecure -H "Content-Type: application/json" --data '
[
        {
        "op": "remove",
        "path": "/users",
        "users": ["jwt_test"]
        }
]
'
{"status":"FORBIDDEN","message":"Resource 'all_access' is static."}

The reason this was not caught is because there currently is no unit test to assert the behavior of the PATCH API to update roles mappings on a static role. There should be a unit test to assert the intended behavior.

[peternied]

As described this is a functional test scenario, why do you think this should be a unit test?

[willyborankin]

@peternied We have such tests in RolesMappingApiTest but they cover only hidden roles verification not reserved and statics both for PUT and PATCH as result it is not clear from tests how it should work.

[stephen-crawford]

[Triage] This PR: #3278, resolved this issue so going to close.