buildroot

docker-engine: bump to version 1.13.1

- Remove patch as it has been applied upstream since 1.13
 - go packages are now in vendor instead of vendor/src so update
slightly the configure and build commands

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>