[CI] Remove var-naming rule from ansible-lint skip

[sdatko]

This change cleans up the code by adding the expected prefix to variables in nfs_server and download_tools roles.

Resolves the following from Ansible-lint run:

WARNING  Listing 11 violation(s) that are fatal
devsetup/nfs.yaml:10: var-naming[no-role-prefix]: Variables names from within roles should use nfs_server_ as a prefix. (vars: nfs_home)
devsetup/roles/download_tools/defaults/main.yaml:3: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: kuttl_version)
devsetup/roles/download_tools/defaults/main.yaml:6: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: opm_version)
devsetup/roles/download_tools/defaults/main.yaml:9: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: oc_mirror_version)
devsetup/roles/download_tools/defaults/main.yaml:12: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: sdk_version)
devsetup/roles/download_tools/defaults/main.yaml:15: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: go_version)
devsetup/roles/download_tools/defaults/main.yaml:18: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: kustomize_version)
devsetup/roles/download_tools/defaults/main.yaml:21: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: kubectl_version)
devsetup/roles/download_tools/defaults/main.yaml:24: var-naming[no-role-prefix]: Variables names from within roles should use download_tools_ as a prefix. (vars: chainsaw_version)
devsetup/roles/nfs_server/defaults/main.yaml:2: var-naming[no-role-prefix]: Variables names from within roles should use nfs_server_ as a prefix. (vars: nfs_home)