Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Change variable in start-new-vm.sh

    Since the patch:

    https://gerrit.opnfv.org/gerrit/#/c/63173/

    The variable BIFROST_USE_PREBUILT_IMAGES has changed to
    BIFROST_CREATE_IMAGE_VIA_DIB. As jenkins does not trigger testing jobs
    when editing file in xci/scripts/, this change is done in a separate
    patch

    Change-Id: I3bc285936fae5b7514272ca0ad2418b60446e4aa
    Signed-off-by: Manuel Buil <mbuil@suse.com>

diff --git a/docs/submodules/releng-xci b/docs/submodules/releng-xci
index fa20640..e340bbd 160000 (submodule)
--- a/docs/submodules/releng-xci
+++ b/docs/submodules/releng-xci
@@ -1 +1 @@
-Subproject commit fa206409872d91bb5c833896357b66a15a39a18a
+Subproject commit e340bbdce220b4f11896267e20981a887ba0c100