Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  to 8b646e9d3cf696db803c937fe014b8a06c68842d
  - Change HEAT package from .tag.gz to be .zip

    As Trevor Lovett suggests, the Heat file is a zip file. So users need to package
    it different only for Dovetail testing.
    It will be better to change it to be .zip to keep it the same as what they do.

    JIRA: DOVETAIL-770

    Change-Id: I5338720c5e1363081e1f8cdce33391a969f1cd97
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 73febf9..8b646e9 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 73febf900b85dae4d953389696f3a78cf8267816
+Subproject commit 8b646e9d3cf696db803c937fe014b8a06c68842d