Check that CHAMELEON_Init() was successful in testing

Hello,

Everything is in the title of the MR / commit message.

You can test it with STARPU_NCPU=1 STARPU_MAIN_THREAD_BIND=1 mpirun ./chameleon_stesting -o potrf. Without my patch, StarPU fails silently in its initialization, but yells and aborts when the first task is submitted. The failure in StarPU initialization is "normal": STARPU_MAIN_THREAD_BIND=1 retrieves one core to the number of cores; and in this case, there is no remaining worker available to execute tasks.

Also I noticed function documentation is not consistent: https://gitlab.inria.fr/solverstack/chameleon/-/blob/master/include/chameleon/runtime.h#L117 says >0 on success to initialize the runtime, while https://gitlab.inria.fr/solverstack/chameleon/-/blob/master/control/control.c#L52 says @retval CHAMELEON_SUCCESS successful exit, it returns well CHAMELEON_SUCCESS in case of success, but CHAMELEON_SUCCESS is defined as 0, which is incoherent with the first comment (or the first comment is incorrect, I don't know ).