Update git submodules

Update git submodules

* Update docs/submodules/apex from branch 'master'
  - Adds deployment via snapshot

    New arguments are added to allow snapshot deployment:
    --snapshot, --snap-cache

    The previous tripleo-quickstart code has been removed/replaced
    with the snapshot option.

    Snapshot deployments are supported on CentOS and Fedora, and snapshot
    artifacts use a similar caching system as the standard deployment.
    Snapshots are produced daily by Apex, and include latest as well as n-1
    OpenStack versions. The os-odl-nofeature scenario is used for the
    snapshots. Additionally multiple topology verions of Snapshots are
    available. The Snapshot pulled at deploy time depends on the
    deploy-settings and number of virtual-computes used at deploy time.

    Since there is only one network used with snapshot deployments (admin),
    there is no reason to pass in network settings for snapshot deployments.
    That argument is now optional. Previously we required even in Standard
    virtual deployments that the network settings be provided. However that
    is also unnecessary, as we can default to the virtual network settings.

    Includes minor fix to the tox.ini to allow specifying test cases
    to run (useful for developers writing tests). Default behavior of
    tox is unchanged.

    JIRA: APEX-548

    Change-Id: I1e08c4e54eac5aae99921f61ab7f69693ed12b47
    Signed-off-by: Tim Rozet <trozet@redhat.com>