Update git submodules

* Update docs/submodules/compass4nfv from branch 'stable/euphrates'
  - Install PBR to ensure we're not breaking builds

    Change-Id: Icd423f469debc4d54b759445f642805c06683bcd
    Signed-off-by: wutianwei <wutianwei1@huawei.com>

diff --git a/docs/submodules/compass4nfv b/docs/submodules/compass4nfv
index 435cd37..f56da9b 160000 (submodule)
--- a/docs/submodules/compass4nfv
+++ b/docs/submodules/compass4nfv
@@ -1 +1 @@
-Subproject commit 435cd3756a833db0515eb70c1d8ec4adca90950f
+Subproject commit f56da9b36698855ad41c95a33612476be0d3cfcc