Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 6b2253fe0008d248f5599f6ef123a55f76336980
  - Merge "Improve kuberef lint script"
  - Improve kuberef lint script

    The OPNFV security audit releng's job prevent to retrieve binaries from
    external sources which results on depending to the binaries provided
    by the OS package managers. This change pretends to cover different
    scenarios where the Jenkins builder is unknown.

    Signed-off-by: Victor Morales <v.morales@samsung.com>
    Change-Id: I37d9b15d3ac9de0b06a96e07eed90f7cc717f444