Add pyzabbix to requirements

PyZabbix is a Python module for working with the Zabbix API.

- Is the library actively maintained?
  Yes.
  here: https://github.com/lukecyca/pyzabbix

- Is the library good code?
  Yes.
  It is stable and runs tests on the different actions it performs.
  We use it in Vitrage project.
  Vitrage: https://wiki.openstack.org/wiki/Vitrage

- Is the library python 3 compatible?
  Yes.

- Is the library license compatible?
  Yes, LGPL.

- Is the library already packaged in the distros we target (Ubuntu
  latest / Fedora latest)?
  There are different rpms for this package.

- Is the function of this library already covered by other libraries
  in ``global-requirements.txt``?
  No.

Change-Id: I8f9f4770295c699b0e023de3d20410494ed704bc

global-requirements.txt

@@ -155,6 +155,7 @@ python-k8sclient>=0.2.0  # Apache-2.0
 voluptuous>=0.8.9  # BSD License
 pydotplus>=2.0.2   # MIT License
 crc16>=0.1.1  # LGPL
+pyzabbix>=0.7.4  # LGPL
 
 # NOTE(flaper87): This added 2 packages to `integration.sh`
 # uuid-dev and swig

projects.txt

@@ -146,6 +146,7 @@ openstack/python-swiftclient
 openstack/python-tackerclient
 openstack/python-tripleoclient
 openstack/python-troveclient
+openstack/python-vitrageclient
 openstack/python-watcherclient
 openstack/python-zaqarclient
 openstack/rally
@@ -176,6 +177,7 @@ openstack/tosca-parser
 openstack/tricircle
 openstack/tripleo-common
 openstack/trove
+openstack/vitrage
 openstack/vmware-nsx
 openstack/watcher
 openstack/zaqar

upper-constraints.txt

@@ -293,6 +293,7 @@ python-troveclient===2.2.0
 python-zaqarclient===1.0.0
 pytz===2016.4
 pyudev===0.20.0
+pyzabbix===0.7.4
 pyzmq===15.2.0
 qpid-python===0.32.1;python_version=='2.7'
 rcssmin===1.0.6