Add new dependency statsd for oslo_middleware

This enables a new middleware that sends wsgi pipeline timing data to
StatsD (and hence Graphite).

It's packaged in all of Ubuntu, CentOS, SuSE and Gentoo, works with
Python 3, looks maintained and has reasonable code quality.

Change-Id: I53dd9116b1c154ffcc3ea2d6b75ecee0061e4866

global-requirements.txt

@@ -179,6 +179,7 @@ vmware-nsxlib>=0.4.0  # Apache-2.0
 pydotplus>=2.0.2   # MIT License
 crc16>=0.1.1  # LGPLv3+
 pyzabbix>=0.7.4  # LGPL
+statsd>=3.2.1  # MIT
 
 # NOTE(flaper87): This added 2 packages to `integration.sh`
 # uuid-dev and swig

upper-constraints.txt

@@ -378,6 +378,7 @@ sqlalchemy-migrate===0.10.0
 sqlparse===0.2.2
 sseclient===0.0.14
 stevedore===1.19.1
+statsd===3.2.1
 suds-jurko===0.6
 sympy===1.0
 sysv-ipc===0.7.0