Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "xci: infra: bifrost: Use XCI virtual environment for bifrost"
  - xci: infra: bifrost: Use XCI virtual environment for bifrost

    We have already prepared a virtual environment for XCI so we may as
    well use it for bifrost as well.

    Change-Id: I084e5da7259a392c5d58e62e7985feb75bb45fb2
    Signed-off-by: Markos Chandras <mchandras@suse.de>

diff --git a/docs/submodules/releng-xci b/docs/submodules/releng-xci
index 73f5018..59678e0 160000 (submodule)
--- a/docs/submodules/releng-xci
+++ b/docs/submodules/releng-xci
@@ -1 +1 @@
-Subproject commit 73f5018ee500401e774c42ea8f32b8db8a5146fd
+Subproject commit 59678e0bad4c4572d6a2933d60e996bcbdad3aa1