TST+DOC: Improve error message for log level, and test HEAVYDEBUG

fail2ban/server/server.py

@@ -336,6 +336,9 @@ class Server:
 			self.__loggingLock.acquire()
 			logging.getLogger(__name__).parent.parent.setLevel(
 				getattr(logging, value.upper()))
+		except AttributeError:
+			raise ValueError("Invalid log level")
+		else:
 			self.__logLevel = value.upper()
 		finally:
 			self.__loggingLock.release()

fail2ban/tests/servertestcase.py

@@ -711,6 +711,7 @@ class TransmitterLogging(TransmitterBase):
 		self.setGetTest("logtarget", "SYSLOG")
 
 	def testLogLevel(self):
+		self.setGetTest("loglevel", "HEAVYDEBUG")
 		self.setGetTest("loglevel", "DEBUG")
 		self.setGetTest("loglevel", "INFO")
 		self.setGetTest("loglevel", "NOTICE")