Tests: metadata env scope values

Tests: metadata env scope values

The tests extract information from the metadata env scope of the trace
and reconstruct an lttng directory hierarchy to validate that the
information found in the metadata is correct.

Testing this way simulate a viewer that must reconstruct a lttng directory
hierarchy from metadata information only. This information is mostly there
for this purpose.

While there we validate the value of other env field when possible.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>