Revert "Monkey patch the source to work with gevent"

This reverts commit 883e57b0.
Drop the greenlet support.

image_creator/dialog_main.py

@@ -33,9 +33,6 @@
 # interpreted as representing official policies, either expressed
 # or implied, of GRNET S.A.
 
-import gevent.monkey  # Monkey-patch everything for gevent early on
-gevent.monkey.patch_all()
-
 import dialog
 import sys
 import os

image_creator/main.py

@@ -33,9 +33,6 @@
 # interpreted as representing official policies, either expressed
 # or implied, of GRNET S.A.
 
-import gevent.monkey  # Monkey-patch everything for gevent early on
-gevent.monkey.patch_all()
-
 from image_creator import __version__ as version
 from image_creator import util
 from image_creator.disk import Disk

setup.py

@@ -46,8 +46,7 @@ setup(
     license='BSD',
     packages=find_packages(),
     include_package_data=True,
-    install_requires=['sh', 'ansicolors', 'progress>=1.0.2', 'py-sendfile',
-        'gevent'],
+    install_requires=['sh', 'ansicolors', 'progress>=1.0.2', 'py-sendfile'],
     entry_points={
         'console_scripts': [
                 'snf-image-creator = image_creator.main:main',