Use non-seam instance of JndiBackedConfig when authenticating via kerberos.

When kerberos authentication happens there is no Seam context available causing the process to fail.
Also revert previous commit which fixed kerberos authentication but broke other authentication mechanisms.
Merge pull request #125 from zanata/kerberos-fix

Use non-seam instance of JndiBackedConfig when authenticating via kerber...
Merge commit 'c75fbd06f35f45e1adb99b8fb4c4e31460b78027' into HEAD