[JENKINS-16273] Improved instructions for passing -jnlpCredentials.

First, display instructions when the user has CONNECT, not necessarily ADMINISTER.
Second, when anonymous users cannot CONNECT, show how to use -jnlpCredentials
(and do not bother showing javaws, since it does not work in this case).(cherry picked from commit a1e709dd)

Conflicts:
	changelog.html