private void cleanupTempDirectory(File tempDir, DeployLogger logger) {
        if (!IOUtils.recursiveDeleteDir(tempDir)) {
            logger.log(Level.WARNING, "Not able to delete tmp dir '" + tempDir + "'");
        }
    }
Gets the active Session for the given application id.

@return the active session, or null if there is no active session for the given application id.
configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java