Tests: add tests for lttng_ust_elf_is_pic

This adds tests for the lttng_ust_elf_is_pic function used to tell
whether an executable is position independent code or not. Three
sample executables are used, one non-PIC executable, one PIE, and a
PIC shared object.

Signed-off-by: Antoine Busque <abusque@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>