MB-31599: Improve audit configuration parsing error messages.
MB-31599: Improve audit configuration parsing error messages.

Modify the way auditd configuration parsing errors are output
so that they are more human readable.

Print the file which threw a json error, a report of what went
wrong, and the content of the file.

New format (with line breaks for commit message):
"2018-10-09T11:16:02.693844Z WARNING Audit::configure:
Audit event configuration error in
"/Users/benhuddleston/Documents/
couchbase/source/build/kv_engine/auditd/audit_events.json".
Error:<ud>[json.exception.out_of_range.403]
key 'modules' not found</ud>).
Content:<ud>...</ud>"

Change-Id: I9ba76f560bfce58ffdd460b40cb4e74ade91883a
Reviewed-on: http://review.couchbase.org/100401
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine