Update git submodules

* Update docs/submodules/apex from branch 'stable/euphrates'
  - Fix RT KVM scenario

    Also change first-boot.yaml to handle updated kernel for rt kvm

    Change-Id: I66b7159731dd286c4a97ba4f3583e229afbb73b3
    Signed-off-by: Feng Pan <fpan@redhat.com>
    (cherry picked from commit 68095d704d1aea94f5890f54eefa13929aab737c)

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 40eedda..924fd4c 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 40eedda05c1757b3b0810ac088c1b067fa325dd1
+Subproject commit 924fd4c07a19029188b315f5aca716b03665f79f