pair.go kept its own copy of the forms a plan may name; the copy in the provisioner client went in #564, after it
refused plans naming `none` while the vault's copy took them. Quick fix and thorough fix are the same here: the vault's
constants are mesh-sdk's (catalogue.CredentialForm*), and a form is judged by catalogue.IsCredentialForm, so a new
form is added in one place. No new test: behaviour is unchanged, and the existing form tests pass on the shared list.
mesh-vault's mesh-sdk pin moves to 9379e9a9, the provisioner client's, the first with the list.
jschoubben
2066021fca