Add custom tags

[helmus]

This is the same pr as #13
Fixes failing tests because of race condition in the bash script, bumps uwsgi to the latest version, build tests from source instead from github

[kitsuyui]

@DataDog
Any update on this?
I want to use this feature too.

[remeh]

Hello @helmus
Thanks for your contribution and sorry for the very late reply.
I've merged #17 which contains custom tags support on top of various other additions. Unfortunately, it won't use the same field name for the configuration, I hope it won't be a problem for you if you switch to use the master branch of uwsgi-dogstatsd. The field name in master is: dogstatsd-extra-tags and tags are comma-separated.
However, I've cherry-picked your commit (to have you as an author of a contribution in the git log) about the tests fix + uwsgi upgrade 👍
Once again, thank you.