Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Delete the updated Alpine image

    It completes "Update Alpine to 3.7" [1].

    [1] https://gerrit.opnfv.org/gerrit/#/c/49741/

    Change-Id: If836a7ca80f5869c9ffeea65a1c0eacf1042ffab
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index ac2c2e1..3b54b93 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit ac2c2e12aad1c4e84dd8df29beeef85611f5cbc8
+Subproject commit 3b54b935c9171891a86d3b7b3bf98eac776ad259