Update git submodules

* Update docs/submodules/apex from branch 'stable/euphrates'
  - Increasing clean.py unittest coverage

    Change-Id: Iae3e80b399d1431382614449488238475b47b103
    Signed-off-by: Dan Radez <dradez@redhat.com>
    (cherry picked from commit 88230c898808ecefffed413c36d3a558dcb7f763)

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 4e73312..e5538af 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 4e7331201ef12419de64061c326604e4a9049be2
+Subproject commit e5538af6b1bf1f6f99b4b288db7ff89c0f6725ea