Update git submodules

* Update docs/submodules/snaps from branch 'master'
  - Fix validate_ssh_client

    After the "try..finally.." statement is executed, the ssh_client is
    closed by the "finally" statement. So the out.channel.in_buffer is
    not readable and the testcases failed.

    Change-Id: I3fbf620cb9ccee62c515b83fed9fd01238ad3262
    Signed-off-by: Alex Yang <yangyang1@zte.com.cn>

diff --git a/docs/submodules/snaps b/docs/submodules/snaps
index 9c023d8..acc4428 160000 (submodule)
--- a/docs/submodules/snaps
+++ b/docs/submodules/snaps
@@ -1 +1 @@
-Subproject commit 9c023d8d1c85650b33e6375d58cd1b45c8d0d395
+Subproject commit acc4428e76422ad5c60f5433f325258214e6bc3b