Allow custom host kernel params for libguestfs

In the libvirt mode of the reproducer script, it may be
very useful to allow customize kernel versions used for
libguestfs commands.

Allow to define those via exported LIBGUESTFS_BACKEND,
SUPERMIN_KERNEL, SUPERMIN_KERNEL_VERSION, SUPERMIN_MODULES
env vars on the virthost.

Change-Id: Ia72b5c2a73e639942dd5182ae8fdc21ab6aa08ef
Signed-off-by: Bogdan Dobrelya <bdobreli@redhat.com>

playbooks/libvirt-nodepool.yml

@@ -17,7 +17,13 @@
   vars:
     - libvirt_nodepool: true
   roles:
-    - libvirt/setup/overcloud
+    - role: libvirt/setup/overcloud
+      environment:
+        SUPERMIN_KERNEL_VERSION: "{{ lookup('env', 'SUPERMIN_KERNEL_VERSION') }}"
+        SUPERMIN_KERNEL: "{{ lookup('env', 'SUPERMIN_KERNEL') }}"
+        SUPERMIN_MODULES:  "{{ lookup('env', 'SUPERMIN_MODULES') }}"
+        LIBGUESTFS_BACKEND: "{{ lookup('env', 'LIBGUESTFS_BACKEND') }}"
+        LIBGUESTFS_BACKEND_SETTINGS: "{{ lookup('env', 'LIBGUESTFS_BACKEND_SETTINGS') }}"
   become: true
 
 - name: Add nodes to the generated inventory