WIP: Events can be defined with no fields yielding no " { } " field text

WIP: Events can be defined with no fields yielding no " { } " field text

The current lttng-modules ctf2 implementation produce the following
"no field" event record:

{
	"type": "event-record-class",
	"id": 0,
	"name": "syscall_entry_gettid"
	"data-stream-class-id": 0,
}

Which is valid and simply result in an output without payload.

In ctf1 the same "event record" is:

event {
        name = "syscall_entry_gettid";
        id = 0;
        stream_id = 0;
        fields := struct {
        };
};

Resulting in an empty but present payload -> " { } "

The tests looked for the presence of a payload ("{.*}"),

For now I decided to modify the regex since I have no feedback from eepp
for the last 5 hours... And ultimately I'm not sure what we should
prioritize in term of preventing "regression".

A ctf2 event record yielding the same output would be:
{
	"type": "event-record-class",
	"id": 0,
	"name": "syscall_entry_gettid"
	"data-stream-class-id": 0,
	"payload-field-class": {
	  "type": "structure"
	}
}

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Change-Id: I42a38d15a2968b278d6ab6625799e5fdcb2d7e53