Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "xci: infra: bifrost: Allow DNS overrides"
  - xci: infra: bifrost: Allow DNS overrides

    Deployers may want to use a different DNS server so allow them to
    override the ipv4_nameserver option. If the variable is not set,
    then we use the libvirt DNS if we are behind a proxy, otherwise
    we default to the Google DNS.

    Change-Id: I96cf63758902d4aae3d155b2e8beef650449ebc9
    Signed-off-by: Markos Chandras <mchandras@suse.de>