python-pip: upgrade 1.5.6 -> 7.1.0

Version numbers are now simply "X.Y" where the leading "1"
has been dropped.
Reference: https://github.com/pypa/pip/blob/develop/CHANGES.txt



Signed-off-by: Li Xin <lixin.fnst@cn.fujitsu.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>