Update git submodules

* Update docs/submodules/compass4nfv from branch 'stable/gambia'
  - Fix LXC apt upgrade issue

    JIRA: -

    Change-Id: I9bf488e4d613d475e833a573635ea5a2ef56aeff
    Signed-off-by: Harry Huang <huangxiangyu5@huawei.com>
    (cherry picked from commit 5a4958ed29c471315c4b54f9a703ff43793688c5)

  - Using images from opnfv repo

    JIRA: -

    Change-Id: If74162f4e5b01fc50d42be5b78ba74f60e173779
    Signed-off-by: Harry Huang <huangxiangyu5@huawei.com>

diff --git a/docs/submodules/compass4nfv b/docs/submodules/compass4nfv
index 4365524..15212e1 160000 (submodule)
--- a/docs/submodules/compass4nfv
+++ b/docs/submodules/compass4nfv
@@ -1 +1 @@
-Subproject commit 436552456ebd857fa1564ba7f15e08ac118fe548
+Subproject commit 15212e1ca1dda0da640dc7f9da14a89c5742fa04