Behavior when failing to dlopen lttng-ust libraries
When debugging the problem described in #1326, I tried setting LTTNG_UST_DEBUG, but didn't see a mention of something going wrong. We should look into what we do when dlopen'ing lttng-ust libraries fails, such as here:
Currently, we silently fail. All the user sees is that tracing doesn't work, and it's quite difficult to know why.