add Principal to subject

Principal is only added to subject if we use RemotingConnectionCredential or when there is no Principal at all.
If we have valid principal we forget about it.

This causes org.jboss.security.auth.spi.RoleMappingLoginModule to be broken.
I'm not sure if this fix is correct (we can always get Principal from callbackHandler in LoginModule).

Another question what to do with roles? (JbossCallbackHandler don't contain this information) and what to do with roles added in LoginModule
[WFLY-2616] Add SEVERE logging level to the valid list of levels.
Revert "Merge commit 'refs/pull/5460/head' of github.com:wildfly/wildfly"

This reverts commit eab955383f9f0647f00e5782998de88600ec62a1, reversing
changes made to 3259a05a2ef9601f3515c5a1cc89f1a9cbd419a3.
Merge pull request #5570 from wojtask9/patch-1

add Principal to subject
Merge pull request #5577 from jamezp/WFLY-2616

[WFLY-2616] Add SEVERE logging level to the valid list of levels.