[release] pagure: 2.15.1

[Pierre-Yves Chibon]

Good Morning Everyone,

I just cut a new release of pagure: 2.15.1

Here is its corresponding changelog:
* Thu May 18 2017 Pierre-Yves Chibon <pingou(a)pingoured.fr&gt; - 2.15.1-1
- Update to 2.15.1
- Fix the requirements on straight.plugin in the requirements.txt file
  (Shengjing Zhu)
- Fix typo in the fedmsg hook so it finds the function where it actually is
- Fix and increase the logging when merging a PR
- Fix pushing a merge commit to the original repo
- Use psutil's Process() instead of looping through all processes (Patrick
  Uiterwijk)
- Don't email admins for each PR conflicting
- Fix/improve our new locking mechanism (Patrick Uiterwijk)
- Drop making the token required at the database level since pagure-ci doesn't
  use one (but do flag pull-requests)
- Fix the watch feature (Matt Prahl)

This is currently happily running in stg.

Happy hacking!
Pierre