Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - fetch_os_creds.sh: Fix unbound BUILD_TAG

    Fuel baremetal deployments provide a certificate, which should be
    copied over to test containers. Virtual deployments do not, hence
    the need to determine the deployment type and decide whether the
    certificate should be transferred in the first place.

    However, the Docker args we contruct will try to map the certificate
    file no matter what, so we will instead try to transfer the cert
    from Salt Master in all deployments, and just create an empty file
    in case it does not exist.

    Change-Id: I3d3fe6cabf552a88841c529ce38446b2e54b3053
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>