Fix Session validation for MCS Operator Mode

[dvaldivia]

Fixes the validation on the Session token for when we are running in MCS_OPERATOR_MODE

also MCS_MKUBE_OPERATOR_ONLY was renamed to MCS_OPERATOR_MODE

[bexsoft]

LGTM

[cesnietor]

testing it

[cesnietor]

please update k8s/base env variable

[cesnietor]

also this env variable needs to be documented

[dvaldivia]

@cesnietor this is a small change that unblocks @bexsoft , I'll update the env but since we no longer have dependencies on mkube I'll send a separate PR removing those dependencies, let's not add more changes to this PR

[cesnietor]

This is happening while trying to log in

│ 2020-07-08T19:25:28.3655455Z 2020/07/08 19:25:28 Get http://m3:8787/api/v1/tenants: dial tcp: lookup m3 on 1 │
│ 2020-07-08T19:25:28.3657217Z 2020/07/08 19:25:28 error login: invalid Credentials  

[dvaldivia]

@cesnietor it's trying to perform a reuqest to m3, which I wanted to address on separate PR, but then I just send the change, bare in mind if you are testing the login using kubectl proxy all requests will succeed, so test the login while running this inside the cluster

[cesnietor]

this is happening:

Request URL: http://localhost:9090/api/v1/login/mkube
Request Method: POST
Status Code: 404 Not Found
Remote Address: [::1]:9090
Referrer Policy: no-referrer-when-downgrade

[cesnietor]

please make one single commit

[dvaldivia]

@cesnietor done

[cesnietor]

please make sure to edit the comments before squashing.