Update git submodules

* Update docs/submodules/snaps from branch 'master'
  - Changed image metadata to support cirros, ubuntu, and centos.

    The image metadata that was designed for multi-part form support
    did not take into account tests that require ubuntu or centos
    tests.

    JIRA: SNAPS-76

    Change-Id: I95c7b74b8f7d7b78c3842b5e716fd7b466107c9c
    Signed-off-by: spisarski <s.pisarski@cablelabs.com>

diff --git a/docs/submodules/snaps b/docs/submodules/snaps
index 58be227..40c9623 160000 (submodule)
--- a/docs/submodules/snaps
+++ b/docs/submodules/snaps
@@ -1 +1 @@
-Subproject commit 58be22735be31d6af00236f36f57dd10e0f9560c
+Subproject commit 40c96233ca4c27de1b3d8b53187c302ddd6208a2