Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge changes I11fdef41,I2b6cf113

    * changes:
      Allow building aarch64 images
      Publish Docker Slicing Presentation

  - Allow building aarch64 images

    It must be noted that Docker automated build cannot create these
    images as the prerequisites are unmet to cross-compile [1].

    It also publishes a travis config file [2].

    [1] https://www.kernel.org/doc/html/v4.11/admin-guide/binfmt-misc.html
    [2] https://travis-ci.org/collivier/functest/builds/286932633

    Change-Id: I11fdef410cc40989132205a098410175f789fdef
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
  - Publish Docker Slicing Presentation

    It published the presentation done in the Functest Breakout during
    last OPNFV Summit (2017 in Beijing) [1].

    Minor changes are planned to update it in a second change.

    Git now ignores pdf which may be generated via reveal.js.

    [1] http://testresults.opnfv.org/functest/dockerslicing/

    Change-Id: I2b6cf113c672320bf1bc34442bb267fd99012546
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index e12d4f1..b31ae2c 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit e12d4f14b65ba08904a65e188db17992478d67a7
+Subproject commit b31ae2c8b59619251cffcba1f307e0b7b9acd89d