Update git submodules

Update git submodules

* Update docs/submodules/releng/builder from branch 'master'
  to f0a041288926db430da904b18a2f8a627248c569
  - Merge "Make xz use multiple threads and lower compression"
  - Make xz use multiple threads and lower compression

    It takes 30 minutes to compress heap dumps in distcheck, this
    patch lowers compression from -9 to -6 (default) and turns on
    multi-threaded compression based on number of cores available.

    Change-Id: I792d6b5c3475262bc16fa0f01726004b7078080c
    Signed-off-by: Robert Varga <robert.varga@pantheon.tech>