Add a json_log option (default: disabled) to logprof.conf that enables
logging of all aa-logprof and aa-genprof input and output to a
/tmp/aa-jsonlog-* file.
This can be useful for debugging, and maybe also to create tests that do
a full aa-logprof run.
This patch introduces a minor behaviour change if aa-logprof errors out
on startup (for example if the config file is broken or the parser can't
be found):
Before:
```
$ aa-logprof --json
{"dialog": "apparmor-json-version","data": "2.12"}
ERROR: Can't find apparmor_parser at /sbin/apparmor_parser
```
After:
```
$ aa-logprof --json
ERROR: Can't find apparmor_parser at /sbin/apparmor_parser
```
Note that the json version line will not be printed if aa-logprof or
aa-genprof error out that early.
If there are no startup errors, the behaviour will not change.
