Make init method of SecurityManager thread safe

javax.jcr.RepositoryException: this session has been closed
at org.apache.jackrabbit.core.SessionImpl.sanityCheck(SessionImpl.java:381)
at org.apache.jackrabbit.core.SessionImpl.getRootNode(SessionImpl.java:788)
at org.hippoecm.repository.security.user.AbstractUserManager.getUser(AbstractUserManager.java:155)
at org.hippoecm.repository.security.SecurityManager.authenticate(SecurityManager.java:133)
at org.hippoecm.repository.security.HippoLoginModule.authenticate(HippoLoginModule.java:252)
at org.junit.Assert.assertTrue(Assert.java:43)
at org.hippoecm.repository.security.HippoLoginModule.login(HippoLoginModule.java:181)
at org.hippoecm.hst.core.jcr.pool.TestBasicPoolingRepository$UncautiousJob.run(TestBasicPoolingRepository.java:254)
at org.apache.jackrabbit.core.security.authentication.LocalAuthContext.login(LocalAuthContext.java:72)
at org.apache.jackrabbit.core.RepositoryImpl.login(RepositoryImpl.java:1356)
at org.hippoecm.repository.jackrabbit.RepositoryImpl.login(RepositoryImpl.java:195)
at org.hippoecm.repository.impl.RepositoryDecorator.login(RepositoryDecorator.java:84)
at org.hippoecm.repository.decorating.checked.RepositoryDecorator.login(RepositoryDecorator.java:77)
at org.hippoecm.hst.core.jcr.pool.TestBasicPoolingRepository$Worker.run(TestBasicPoolingRepository.java:222)
at org.hippoecm.repository.HippoRepositoryImpl.login(HippoRepositoryImpl.java:113)
at org.hippoecm.repository.HippoRepositoryImpl.login(HippoRepositoryImpl.java:126)
at org.hippoecm.hst.core.jcr.pool.JcrHippoRepository.login(JcrHippoRepository.java:124)
at org.hippoecm.hst.core.jcr.pool.BasicPoolingRepository$SessionFactory.makeObject(BasicPoolingRepository.java:878)
at org.apache.commons.pool.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:974)
Exception in thread "Thread-35" java.lang.AssertionError: No waiting occurred.