Fix: tests: skip UST perf tests if not root

Fix: tests: skip UST perf tests if not root

Some distributions like Debian (e.g. Debian kernel 4.1.0-2-amd64) have
some grsecurity options enabled, such as CONFIG_GRKERNSEC_PERF_HARDEN.

Unfortunately, this option makes it impossible to use the SW page-fault
perf event as a normal user. It only leaves some HW events. However, we
can only use SW events within virtual machines.

Therefore, only run this test as root for now until we find a better
approach.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>