Update git submodules

* Update docs/submodules/apex from branch 'stable/euphrates'
  - Fixes removing inventory keys

    Inventory keys that we want to delete were not being removed for
    instackenv.json.  Also fixes unit tests.

    Change-Id: I7d6c752342db050d651953633f18e236f60334e3
    Signed-off-by: Tim Rozet <trozet@redhat.com>
    (cherry picked from commit 17d5b541e93f5d88ff958372cdf0b0b184bdbc27)

diff --git a/docs/submodules/apex b/docs/submodules/apex
index f9d02c0..8cafb28 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit f9d02c076974168677bf5fdb02f26caf73924fb8
+Subproject commit 8cafb288943dd0ad9a29c6e7b3d7b22710a10f89