ERROR instead of INFO

fixes #2132
Made a nicer message

With a little clarification: if voms returned an actual error, then there is a real problem. If it's just because voms-proxy-init isn't present, then only show the notice.
Fixed res -> result

Also conventions.
Check existence of voms-proxy- commands

And return S_ERROR if they aren't there.
explicit handling of missing voms-proxy-XX cmds
Merge pull request #2133 from sposs/patch-6

[v6r12] ERROR instead of INFO for error while adding VOMS extension