external: do not enforce rbd, cephfs and rgw flags for the external cluster

[parth-gr]

there might be a user who only wants to use rbd, so don't enforce them
to to create all the pools and pass the flags

Closes: #11846

Description of your changes:

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[travisn]

Please also add a brief description paragraph in the commit message and the PR description that describes more the changes.

[travisn]

LGTM. I see the CI is passing for the external tests, but before we merge, can you comment on how you could test the changes?

[parth-gr]

LGTM. I see the CI is passing for the external tests, but before we merge, can you comment on how you could test the changes?

Basically, run the script on any rook cluster,
And check if we don't give cephfs for example then it won't complain for it and would be succeeded

[parth-gr]

Tested,
It worked

[rider@localhost ~]$ ./a.sh
secret/rook-ceph-mon created
configmap/rook-ceph-mon-endpoints created
secret/rook-csi-rbd-node created
secret/rook-csi-rbd-provisioner created
storageclass.storage.k8s.io/ceph-rbd created