Default values for perflog format is not accurate in the docs

[vkarak]

The default perflog handler's format is stated to be "%(message)s" and the format_perfvars, but this is not true. These are defined in the builting configuration file differently:

reframe/reframe/core/settings.py

Lines 52 to 94 in 8000b58

	'handlers_perflog': [
	{
	'type': 'filelog',
	'prefix': '%(check_system)s/%(check_partition)s',
	'level': 'info',
	'format': ('%(check_result)s|'
	'%(check_job_completion_time)s|%(check_#ALL)s'),
	'ignore_keys': [
	'check_build_locally',
	'check_build_time_limit',
	'check_display_name',
	'check_executable',
	'check_executable_opts',
	'check_hashcode',
	'check_keep_files',
	'check_local',
	'check_maintainers',
	'check_max_pending_time',
	'check_outputdir',
	'check_prebuild_cmds',
	'check_prefix',
	'check_prerun_cmds',
	'check_postbuild_cmds',
	'check_postrun_cmds',
	'check_readonly_files',
	'check_sourcepath',
	'check_sourcesdir',
	'check_stagedir',
	'check_strict_check',
	'check_tags',
	'check_time_limit',
	'check_valid_prog_environs',
	'check_valid_systems',
	'check_variables'
	],
	'format_perfvars': (
	'%(check_perf_value)s|%(check_perf_unit)s|'
	'%(check_perf_ref)s|%(check_perf_lower_thres)s|'
	'%(check_perf_upper_thres)s|'
	),
	'append': True
	}
	]

We should update the docs.

[vkarak]

I took another look. The docs are not wrong here, as the default would indeed be what it is being written if the users override the default handlers_perflog. I think we should add instead a section describing/showing the builtin configuration.