Tests: Add UST snapshots list output and max-size tests

Add two new tests to the UST snapshots tests:

test_ust_list_output:
Add/remove named outputs and validate with the list output command.

test_ust_local_snapshot_max_size:
Take a UST snapshot with max-size limits and validate that they are respected.

Signed-off-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Tests: Add UST snapshots streaming test with custom URI

Signed-off-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>