log: enhance gluster log format with message ID and standardize errno reporting

	Currently there are quite a slew of logs in Gluster that do not
	lend themselves to trivial analysis by various tools that help
	collect	and monitor logs, due to the textual nature of the logs.

	This FEAT is to make this better by giving logs message IDs so
	that the tools do not have to do complex log parsing to break
	it down to problem areas and suggest troubleshooting options.

	With this patch, a new set of logging APIs are introduced that
	take additionally a message ID and an error number, so as to
	print the message ID and the descriptive string for the error.

	New APIs:
		- gf_msg, gf_msg_debug/trace, gf_msg_nomem, gf_msg_callingfn

	These APIs follow the functionality of the previous gf_log*
	counterparts, and hence are 1:1 replacements, with the delta
	that, gf_msg, gf_msg_callingfn take additional parameters as
	specified above.

	Defining the log messages:
	Each invocation of gf_msg/gf_msg_callingfn, should provide an ID
	and an errnum (if available). Towards this, a common message id
	file is provided, which contains defines to various messages and
	their respective strings. As other messages are changed to the
	new infrastructure APIs, it is intended that this file is edited
	to add these messages as well.

	Framework enhanced:
	The logging framework is also enhanced to be able to support
	different logging backends in the future. Hence new configuration
	options for logging framework and logging formats are introduced.

	Backward compatibility:
	Currently the framework supports logging in the traditional
	format, with the inclusion of an error string based on the errnum
	passed in. Hence the shift to these new APIs would retain the log
	file names, locations, and format with the exception of an
	additional error string where applicable.

	Testing done:
	Tested the new APIs with different messages in normal code paths
	Tested with configurations set to gluster logs (syslog pending)
	Tested nomem variants, inducing the message in normal code paths
	Tested ident generation for normal code paths (other paths
		pending)
	Tested with sample gfapi program for gfapi messages
	Test code is stripped from the commit

	Pending work (not to be addressed in this patch (future)):
	- Logging framework should be configurable
	- Logging format should be configurable
	- Once all messages move to the new APIs deprecate/delete older
	  APIs to prevent misuse/abuse using the same
	- Repeated log messages should be suppressed (as a configurable
	  option)
	- Logging framework assumes that only one init is possible, but
	  there is no protection around the same (in existing code)
	- gf_log_fini is not invoked anywhere and does very little
	  cleanup (in existing code)
	- DOxygen comments to message id headers for each message

Change-Id: Ia043fda99a1c6cf7817517ef9e279bfcf35dcc24
BUG: 1075611
Signed-off-by: ShyamsundarR <srangana@redhat.com>
Reviewed-on: http://review.gluster.org/6547
Reviewed-by: Krutika Dhananjay <kdhananj@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>