Plugin test cleanup (#1479)

* Autotools plugin test cleanup

* Combines filter, VFD, and VOL plugin tests
* Adds VFD plugin tests to the Autotools
* Implements a uniform shell script naming scheme in test/

* codespell fix

* Changes after code review

test/filter_plugin.c

@@ -968,16 +968,6 @@ test_path_api_calls(void)
      */
     n_starting_paths = 42;
 
-    /* Check that initialization is correct */
-    TESTING("    initialize");
-
-    if (H5PLsize(&n_paths) < 0)
-        TEST_ERROR;
-    if (n_paths != 2)
-        TEST_ERROR;
-
-    PASSED();
-
     /****************/
     /* H5PLremove() */
     /****************/