Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Update cirros image for bottlenecks

    The fraser-based OPNFV tools use the newer cirros-0.4.0 image and we
    hence only ask users to download this version in the user guide.
    This updates the bottlenecks test to comply with this.

    Change-Id: I5a94d6a7196ae04e00150dc17a4a16add2d3fef6
    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index edf504a..21cc3e2 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit edf504a4071b1d9300f72c5d83a22cda3bf2dc67
+Subproject commit 21cc3e247b7ecbd8dd030c1a6c951cfbcf3c9d05