Changed 'xml' to 'XML'

Like Lana Brindley mentioned in https://review.openstack.org/#/c/102900/
'xml' should be 'XML' instead.

Change-Id: If500ec9325eff98d58810b69c6fc84211e20638a
Sync with oslo

This brings some bugfixes for Python 3 support.

Sync with 468afcb335a98dcfdc1520a73937982107bc2758

Change-Id: Ida73ae17b945e084a52b7024a91707f7729adfa1
Found a useless comment

It seems to be legacy of debug steps done by the developer.

Change-Id: I84484619803b3006583b70c7a49039e9c2924ce6
Add CONTRIBUTING.rst

There is no CONTRIBUTING.rst file, the patch will add it.

Change-Id: Ia54b37845dddcd6d8962f4493d5f9906e5604288
Merge "Changed 'xml' to 'XML'"
Merge "Found a useless comment"
Merge "Add CONTRIBUTING.rst"