Newer versions of the sdist plugin do not resolve pytz properly

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When using com.linkedin.python-sdist > 0.4.9 the build always fails inside of installBuildRequirements with
```
Processing /home/vagrant/.gradle/caches/modules-2/files-2.1/pypi/Sphinx/1.4.1/d18b856710b22ae9740147e21754ca5b851af9b2/Sphinx-1.4.1.tar.gz
Complete output from command python setup.py egg_info:
Traceback (most recent call last):
File "", line 20, in
File "/tmp/pip-1phE1A-build/setup.py", line 79, in
from babel.messages.pofile import read_po
File "/home/vagrant/dev/xxx/build/venv/local/lib/python2.7/site-packages/babel/messages/__init__.py", line 12, in
from babel.messages.catalog import *
File "/home/vagrant/dev/xxx/build/venv/local/lib/python2.7/site-packages/babel/messages/catalog.py", line 23, in
from babel.dates import format_datetime
File "/home/vagrant/dev/xxx/build/venv/local/lib/python2.7/site-packages/babel/dates.py", line 28, in
from babel.util import UTC, LOCALTZ
File "/home/vagrant/dev/xxx/build/venv/local/lib/python2.7/site-packages/babel/util.py", line 282, in
UTC = _pytz.utc
AttributeError: 'module' object has no attribute 'utc'
```

Start by reproducing installBuildRequirements with com.linkedin.python-sdist greater than 0.4.9 and inspect the plugin's dependency-resolution path for pytz. The issue is done when the build installs its requirements without the shown Babel/pytz AttributeError.

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