Increased the minimum version of pip to 6.1.1 -- 6.0 doesn't seem to deal well with virtualenv with --system-site-packages.

 - Legacy-Id: 12193

Author: levkowetz

requirements.txt

@@ -22,7 +22,7 @@ mock>=2.0.0
 MySQL-python>=1.2.5
 pathlib>=1.0
 Pillow>=3.0
-pip>=6.0
+pip>=6.1.1
 pyang>=1.6
 pyflakes>=0.8.1
 pyquery>=1.2.13,!=1.2.14	# Pyqyery 1.2.14 fails on some selectors or stacked selectors