Update git submodules

* Update docs/submodules/apex from branch 'stable/euphrates'
  - Merge "baro: update collectd-openstack branch" into stable/euphrates
  - baro: update collectd-openstack branch

    COLLECTD_OPENSTACK_GIT_BRANCH has been updated to stable/pike so that aodh
    changes will be picked up

    Previously, the branch was not actually being checked out, but was being
    used as a name for a new branch. This behaviour has been corrected.

    Change-Id: I516c4311d2a0cedcca6ec293b62c21234b1e1975
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 43f65e1..6e7af7e 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 43f65e19443168ea7ab1d372902318c0129d6306
+Subproject commit 6e7af7e195f509a6658d65874ff179568ff8fda4