Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Merge "Doc: update user guide due to add new test cases and features"
  - Doc: update user guide due to add new test cases and features

    There has been added some new test cases and features, so user guide should be
    updated according to the latest dovetail version.
    - Add introduction about https (with cacert and without cacert)
    - Add introduction about adding hosts' info
    - Add introduction about downloading cirros images
    - Add introduction about special configurations for running defcore and
      tempest test cases
    - Add introduction about how to check defcore and tempest failed test cases

    JIRA: DOVETAIL-493

    Change-Id: I13aca4ee433056bd21590743a412d5d95f45fec4
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 0aacdce..26e9f22 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 0aacdceeeac62333651ec5440fb32af965c7689e
+Subproject commit 26e9f2236ae2bcc8e14e5d4c32b883df188f1356