test: let qemuhotplugtest report details of init fails

If virHostdevManagerGetDefault in qemuhotplugtest fails it works
for quite a while to later segfault when accessing
mgr->activePCIHostdevs.

Report the error details and break on a failed init to see the
real issue right away.
Reviewed-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NChristian Ehrhardt <christian.ehrhardt@canonical.com>

tests/qemuhotplugtest.c

@@ -634,6 +634,11 @@ mymain(void)
         return EXIT_FAILURE;
 
     driver.hostdevMgr = virHostdevManagerGetDefault();
+    if (driver.hostdevMgr == NULL) {
+        VIR_TEST_VERBOSE("Could not initialize HostdevManager - %s\n",
+                         virGetLastErrorMessage());
+        return EXIT_FAILURE;
+    }
 
 
 #define DO_TEST(file, ACTION, dev, fial, kep, ...) \