Update git submodules

* Update docs/submodules/doctor from branch 'master'
  - Merge "bugfix: kill the stunnel when cleanup"
  - bugfix: kill the stunnel when cleanup

    Popen.terminate() will kill the child process, but if you set the
    shell argument to True, this is the process ID of the spawned shell,
    so the stunnels are still exit.It will cause the failure of stunnel
    setup in the next test runtime.

    see: https://stackoverflow.com/questions/4789837/how-to-terminate-a-python-subprocess-launched-with-shell-true/4791612#4791612

    Change-Id: I578611510f5bd1eb0dbd9a08ab408ccf101594f7
    Signed-off-by: dongwenjuan <dong.wenjuan@zte.com.cn>

diff --git a/docs/submodules/doctor b/docs/submodules/doctor
index eaeb3c0..b2bb504 160000 (submodule)
--- a/docs/submodules/doctor
+++ b/docs/submodules/doctor
@@ -1 +1 @@
-Subproject commit eaeb3c0f9dc9e6645a159d0a78b9fc181fce53d4
+Subproject commit b2bb504032ac81a2ed3f404113b097d9ce3d7f14