Update Build state at the end of UpdateDocsTask.run (#3293)
Update Build state at the end of UpdateDocsTask.run (#3293)

* Update Build state at the end of UpdateDocsTask.run

Use the `update_build` method that handles most of the cases but fill
the `failure` with a unhandled exception in case it was risen.

* Fix lint style

* Fix attribute name

* Return the object we already have in memory instead of doing API call

* Use a str variable

davidfischer/readthedocs.org,rtfd/readthedocs.org,davidfischer/readthedocs.org,davidfischer/readthedocs.org,davidfischer/readthedocs.org,pombredanne/readthedocs.org,safwanrahman/readthedocs.org,pombredanne/readthedocs.org,safwanrahman/readthedocs.org,rtfd/readthedocs.org,safwanrahman/readthedocs.org,rtfd/readthedocs.org,safwanrahman/readthedocs.org,rtfd/readthedocs.org,pombredanne/readthedocs.org