xtarfile: vendor, rather than lib

since the 'xtarfile' is really just a vendored copy of stdlib 'tarfile',
move it out of ./lib/ to a directory called vendor.
This also helps with the coverage analysis (since it does an inclusive
mask over ./lib)

Docker-DCO-1.1-Signed-off-by: Vincent Batts <[email protected]> (github: vbatts)

Author: vbatts

docker_registry/images.py

@@ -19,7 +19,7 @@
 from .lib import checksums
 from .lib import layers
 from .lib import mirroring
-from .lib import xtarfile
+from .vendor import xtarfile
 
 
 store = storage.load()

docker_registry/lib/layers.py

@@ -11,7 +11,7 @@
 from . import cache
 from . import rqueue
 # this is our vendored 'tarfile' from python v2.7.6, with xattr support
-from . import xtarfile
+from ..vendor import xtarfile
 
 
 store = storage.load()