[WFCORE-128] New test to reproduce failure where users is referencing a non-existent group.
[WFCORE-128] Fixed an issue where a non-existent ldap group causes an authentication attempt to fail in a security-realm
[WFCORE-128] Skip groups that are missing where principal to group mappings are being used with LDAP.
[WFCORE-128] Schema changes to support skipping missing groups during group loading.