Found additional pip versions that are broken. Limiting pip to 9.0.1 for now.

 - Legacy-Id: 15003

Author: levkowetz

requirements.txt

@@ -35,7 +35,7 @@ patch>=1.16,<2.0
 pathlib>=1.0
 pathlib2>=2.3.0
 Pillow>=3.0
-pip>=9.0.1,!=9.0.2,!=9.0.3	# Earlier pip has issues, 9.0.2 and 9.0.3 leaves dross when down- and up-grading packages
+pip==9.0.1			# Earlier pip has issues, 9.0.2 and 9.0.3, 10.0.0b1 leaves dross when down- and up-grading packages
 pyang>=1.7.2,<2.0
 pyflakes>=0.9.2
 pyopenssl>=17.5.0		# Used by urllib3.contrib, which is used by PyQuery but not marked as a dependency