Use ssh instead of VBoxManage to execute tests

VBoxManage requires a socket in /tmp,
which is not compatible with PrivateTmp=true of systemd.exec(5).

VBoxManage is not reliable anyway. (it's buggy)
added libass-build
autoconf: do not use rpl_malloc()
temporary patches for mpv on Win32
Fixed mpv-build since upstream now use waf
Removed libvpx from ffmpeg

ffmpeg 2.1 now has native VP9 decoder.