Functional tests without MPI support (#343)

* Let functional tests build without external MPI

* Fix error conditions when using uuid startup with internal MPI

* Do not abort if libibverbs is not found but not using GDA

* Enabled RO functional test initialized with TEST_UUID

* Reduce load time for ro backend_can_run and prevent mpilib_dlclose
crashing

* Fix case TEST_UUID=1, ROCSHMEM_BACKEND='' (autoloading gda)

[ROCm/rocshmem commit: c99bc21e10]

projects/rocshmem/src/mpi_instance.cpp

@@ -138,6 +138,9 @@ void MPIInstance::mpilib_dl_close() {
 
 MPIInstance::MPIInstance(MPI_Comm comm) {
   int is_init{0};
+
+  assert (nullptr != mpilib_handle_);
+
   mpilib_ftable_.Initialized(&is_init);
 
   if (!is_init) {