Add UST test for n events using validation

ust-nevents tests an instrumented application generating 100 events and
validating that those events are found using babeltrace (need to be
installed).

Adds the tests/utils.sh which is a family of function used to interact
with lttng cli. There is also a trace_matches function which uses
babeltrace to find string patterns.

Also, the session daemon is spawned at the beginning of runall.sh and
killed at the end. This means that all tests are done on a single
session daemon instance. Thus, session name across tests have to be
unique! From now on, each test should use the file name as a unique
identifier for the session name.

Finally, fixed the session name for all tests. At this commit, "make
check" or "sudo make check" should pass.

Signed-off-by: David Goulet <dgoulet@efficios.com>