Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "xci: Adjust how bifrost inventory files are specified"
  - xci: Adjust how bifrost inventory files are specified

    First step towards creating env-vars files based on the use of these
    scripts so the scripts can be merged into one.

    Change-Id: I4ee1d9af520aa684a5367a2645d709835bc4a5a1
    Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index e87c89a..8b15725 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit e87c89a144107c0f764458942a174e4563082f03
+Subproject commit 8b15725dc3a5df11bb3f62b054ee5454f4506ba4