Set SUPERMIN_* variables to working kernel

virt-customize(libguestfs) is not working with current
kernel 3.10.0-693.11.6.el7 in centos.
So until it's fixed in libguestfs or kernel, let's
use working kernel 3.10.0-693.el7.x86_64.
The kernel version is managed using following variable
which can be overridden when required.
Libguesfs requires following environment variables
to use the overridden kernel.

- SUPERMIN_KERNEL_VERSION: {{ libguestfs_kernel_override }}
- SUPERMIN_KERNEL: /boot/vmlinuz-{{ libguestfs_kernel_override }}
- SUPERMIN_MODULES: /lib/modules/{{ libguestfs_kernel_override }}

Change-Id: I129ec6c48d801cd605c4befda5ee00a025480413
Partial-Bug: #1743749

roles/modify-image/defaults/main.yml

@@ -27,3 +27,4 @@ modify_image_vc_trace: false
 libguestfs_mode: true
 # TODO(sshnaidm): implement initramfs image modifying
 initramfs_image: false
+libguestfs_kernel_override: 3.10.0-693.el7.x86_64

roles/modify-image/tasks/libguestfs.yml

@@ -44,6 +44,11 @@
     > {{ working_dir }}/{{ modify_script|default('modify_image')|replace('/','_') }}.log 2>&1
   environment:
     LIBGUESTFS_BACKEND: direct
+    # FIXME(ykarel) SUPERMIN_* can be removed once
+    # https://bugs.launchpad.net/tripleo/+bug/1743749 is completely fixed.
+    SUPERMIN_KERNEL_VERSION: "{{ libguestfs_kernel_override }}"
+    SUPERMIN_KERNEL: "/boot/vmlinuz-{{ libguestfs_kernel_override }}"
+    SUPERMIN_MODULES: "/lib/modules/{{ libguestfs_kernel_override }}"
   args:
     chdir: "{{ modify_image_working_dir }}"