Revert "Drop x86-TF-06"

This reverts commit 0a92715ac3925b12e30d65f5e30b26a04d9f948e.

Reason for revert: x86-TF-06 still exists, and used for builds. It thus needs to have docker images, etc. updated. See https://linaro.atlassian.net/browse/STG-5588

Change-Id: Id2661a92fd660d5377fc23ad19a087951002a389
diff --git a/ci-dockerslaves-cleanup.yaml b/ci-dockerslaves-cleanup.yaml
index edffffa..ae90a38 100644
--- a/ci-dockerslaves-cleanup.yaml
+++ b/ci-dockerslaves-cleanup.yaml
@@ -35,6 +35,7 @@
                 - x86_64-TF-03
                 - x86_64-TF-04
                 - x86_64-TF-05
+                - x86-TF-06
     execution-strategy:
         sequential: false
     wrappers: