Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - patches: libvirt: Use "libvirt" unix_sock_group

    Now that libvirt 3.6 is used on kvm nodes (via UCA repos), which
    by default uses "libvirt" group for socket ownership,
    change old "libvirtd" in salt-formula-libvirt's:
    - libvirt/files/libvirtd.conf.Debian

    This allows us to remove the manual group creation from VCP state
    file, which was not re-entrant (failed if group already existed).

    Change-Id: Id61fecd82daec1c0716ff4796b79dce47d096c3a
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index b49bc80..7938017 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit b49bc80c8a491a88ddb93ce6f60ba73a208fdd4f
+Subproject commit 7938017cfc501b9809d8ce95da614c7f7e849d5d