Update git submodules

* Update docs/submodules/apex from branch 'stable/danube'
  - Fixes vars missing in overcloudrc.v3

    Change-Id: I03df4973fe2bb1356719dda5666484f556df2ffa
    Signed-off-by: Tim Rozet <trozet@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index f4f6eea..abb2b6f 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit f4f6eeab383e808caa4756fc8c31fe684983b234
+Subproject commit abb2b6f9008c7661aa0aaeb12a58aeba02106eaa