Tests: Add callstack contexts tests

Tests callstack-user and callstack-kernel contexts by tracing with those
contexts an application that calls multiple functions in chain before
executing a system call.

callstack-user addresses are tested against the output of coreutils'
addr2line.
callstack-kernel addresses are tested against the addresses of kernel
symbols available in the /proc/kallsyms procfile.

Both these tests need to be run by root because those contexts are made
available by the kernel tracer. The callstack-kernel test also need to
access /proc/kallsyms.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>