Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Merge "standardize ssh auth" into stable/danube
  - standardize ssh auth

    we need to be following defautl paramiko rules,
    first use pkey, then key_filenames (autodetecting ~/.ssh/ keys),
    then password

    We have too much boilerplate redudant code everywhere, we need
    to standardize on a factory function that takes a node dict.

    Using Python3 ChainMap we can layer overrides and defaults.

    VNF descriptors have to default key_filename, password to Python None.
    The only way to do this is to omit key values if the variable is not
    defined, this way the dict will not have the value and it will
    default to Python None

    Add python2 chainmap backport

    Updated unittest mocking to use ssh.SSH.from_node

    Change-Id: I80b0cb606e593b33e317c9e5e8ed0b74da591514
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>
    (cherry picked from commit 99abbb424007da2e01762f3c040a39c0157cbe1f)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 058f0a9..20f5b0a 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 058f0a93fd37694b74c5f1414bdfa6b35114690a
+Subproject commit 20f5b0a8580c0e8c659424bab434a0e30f3c88c1