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)

tests/functional_tests/test_driver.cpp

@@ -172,6 +172,9 @@ int main(int argc, char *argv[]) {
     char key[] = "rocshmem-uuid";
     pmix_bcast(&uid, sizeof(rocshmem_uniqueid_t), key, 0);
 
+    // Close PMIx before potentially doing MPI_Init inside rocshmem_init
+    PMIx_Finalize(NULL, 0);
+
     ret = rocshmem_set_attr_uniqueid_args(rank, nranks, &uid, &attr);
     if (ret != ROCSHMEM_SUCCESS) {
       std::cout << rank << ": Error in rocshmem_set_attr_uniqueid_args. Aborting.\n";
@@ -224,11 +227,5 @@ int main(int argc, char *argv[]) {
    */
   rocshmem_finalize();
 
-#ifdef HAVE_PMIX
-  if (test_uuid) {
-    PMIx_Finalize(NULL, 0);
-  }
-#endif
-
   return 0;
 }