Update git submodules

Update git submodules

* Update docs/submodules/daisy from branch 'stable/euphrates'
  - Merge "Use pxe bridge to replace the bridge in VM template" into stable/euphrates
  - Use pxe bridge to replace the bridge in VM template

    1. Eliminate hard code about pxe bridge
    2. Replace the bridge in daisy VM template with the pxe bridge
    provided by jenkins

    Change-Id: I7a8463181847417d10705ce9ff4db6e68d505c6d
    Signed-off-by: Alex Yang <yangyang1@zte.com.cn>
    (cherry picked from commit 56975272e92efa3f5f6f719028dc147c1d90e9ce)