Resolve Coverity CHECKED_RETURN

Coverity complained that checking the return of virDomainCreate()
was not consistent amongst the callers - so added the return check
to the objecteventtest.c and adjust the virt-login-shell to compare
< 0 rather than just non zero for the failure condition.

tests/objecteventtest.c

@@ -359,7 +359,8 @@ testDomainStartStopEvent(const void *data)
 
     /* Test domain is started */
     virDomainDestroy(dom);
-    virDomainCreate(dom);
+    if (virDomainCreate(dom) < 0)
+        goto cleanup;
 
     if (virEventRunDefaultImpl() < 0)
         goto cleanup;

tools/virt-login-shell.c

@@ -275,7 +275,7 @@ main(int argc, char **argv)
     if (!dom)
         goto cleanup;
 
-    if (!virDomainIsActive(dom) && virDomainCreate(dom)) {
+    if (!virDomainIsActive(dom) && virDomainCreate(dom) < 0) {
         virErrorPtr last_error;
         last_error = virGetLastError();
         if (last_error->code != VIR_ERR_OPERATION_INVALID) {