Change python-nose package name in devstack

In RedHat8, python-nose is separated to 2 packages of
python2 and python3.
This patch changed devstack plugin to use the separated packages.

Change-Id: I1a3608a52c37718715cdfecc8cc2d4a7e76b1714

devstack/plugin.sh

@@ -127,7 +127,15 @@ function install_mistral {
     setup_develop $MISTRAL_DIR
 
     # installing python-nose.
-    real_install_package python-nose
+    if is_fedora; then
+	if python3_enabled; then
+            real_install_package python3-nose
+	else
+            real_install_package python2-nose
+        fi
+    else
+        real_install_package python-nose
+    fi
 
     if is_service_enabled horizon; then
         _install_mistraldashboard