Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Vagrantfile: Bump memory requirements to 16G

    Apparently 8G is no longer enought to deploy the 'mini'
    flavor since the following error occurs:

    [14505.101254] Out of memory: Kill process 23666 (qemu-system-x86) score 344 or sacrifice child
    [14505.103404] Killed process 23666 (qemu-system-x86) total-vm:5566132kB, anon-rss:3008288kB, file-rss:0kB, shmem-rss:0kB

    Change-Id: Iaa21ad367c63bf17a2c999082b5e09fa2e772d67
    Signed-off-by: Markos Chandras <mchandras@suse.de>