small improvements to bot...

[trz42]

In #359 we found that for some strings hardcoded values are used instead of constants. See

eessi-bot-software-layer/tools/job_metadata.py

Lines 107 to 110 in 6b00963

	bot_jobfile[JOB_PR_SECTION] = {'repo': repo_name,
	'pr_number': pr_number,
	'pr_comment_id': pr_comment_id,
	'job_owner': job_owner}

Also, we could order the currently supported commands alphabetically. See

eessi-bot-software-layer/eessi_bot_event_handler.py

Line 513 in 6b00963

help_msg += "\n - Currently supported COMMANDs are: `help`, `build`, `show_config`, `status`, `cancel`"