Delaying LOG4CXX initialization until first actual use (DM-6989)

[andy-slac]

Previously LOG4CXX was initialized at DSO loading time (at globals
initialization time) which caused issues with global destructors
ordering. This patch delays initialization until first actual use of
logging methods which partially resolves the issue (there are still
possible use cases when the problems can re-appear).

Also some cleanup to macros for efficiency and simplicity after recent
changes to Log class.

Re-applied previous commit from DM-6521 - "Replace defaultLogger by a static method getDefaultLogger()"

[RobertLuptonTheGood]

I'm guessing that you're using a singleton?

It'd be good to elaborate on:
bq. there are still possible use cases when the problems can re-appear
(does this refer to multithreading?)

[andy-slac]

@RobertLuptonTheGood, indeed there is a singleton which is used as a default logger instance. That is not a problem by itself though, because there are globals in both LOG4CXX and activemq which are actual problem.

JIRA ticket (DM-6989) has an example of a use case when things may still break even after this fix. The problem is with a global root logger in LOG4CXX which keeps appender instantiated by ctrl_events which uses activemq (with its globals). Normally ctrl_events and activemq should be loaded before root logger is instantiated and when globals are destroyed the order is correct in a sense that root logger and its appenders are destroyed before activemq globals. But it is possible to break this order if one manages to instantiate root logger first and then load ctrl_events and activemq. Simplest example is like this:

import lsst.log as log
log.debug("lsst.log is imported")    # this will initialize log4cxx and create root logger
import lsst.ctrl.events              # this will instantiate activemq globals
# instantiate ctrl_events log appender via re-configuring log4cxx

With this use case the order of destruction is reversed, activemq globals will be destroyed first, then root logger is destroyed which calls appender destructor which tries to access activemq globals. The fix for this problem should be possible in ctrl_events.