Update git submodules

Update git submodules

* Update docs/submodules/apex from branch 'stable/euphrates'
  - Fixes dependency install of env group Virtualization Host

    Virtualization Host env group started failing for users with centos 7.4
    and according to Ansible guide the correct format for env groups should
    be "@^" prefix:

    http://docs.ansible.com/ansible/latest/yum_module.html

    JIRA: APEX-539

    Change-Id: I3f71ce4462b33ad0772963869db4ea3c0f6e9e51
    Signed-off-by: Tim Rozet <trozet@redhat.com>
    (cherry picked from commit c4fe041a2cfd586a7b6897c7fbe15c8efb5aef32)