Add "pip" to the python:2 image since it isn't included upstream

[tianon]

Fixes #1

[tianon]

$ docker build -t infosiftr/python:2 2
...
rm -f /usr/local/share/man/man1/python2.1
(cd /usr/local/share/man/man1; ln -s python2.7.1 python2.1)
rm -f /usr/local/share/man/man1/python.1
(cd /usr/local/share/man/man1; ln -s python2.1 python.1)
find . -name '*.py[co]' -exec rm -f {} ';'
find . -name '*.[oa]' -exec rm -f {} ';'
find . -name '*.s[ol]' -exec rm -f {} ';'
find . -name '*.so.[0-9]*.[0-9]*' -exec rm -f {} ';'
find build -name 'fficonfig.h' -exec rm -f {} ';' || true
find build -name 'fficonfig.py' -exec rm -f {} ';' || true
rm -f Lib/lib2to3/*Grammar*.pickle
 ---> 553508b7dd1d
Removing intermediate container 537c3e8f01c3
Step 7 : RUN curl -SL 'https://bootstrap.pypa.io/get-pip.py' | python2
 ---> Running in bb7d99b3532c
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 1309k  100 1309k    0     0   921k      0  0:00:01  0:00:01 --:--:--  921k
Downloading/unpacking pip
Downloading/unpacking setuptools
Installing collected packages: pip, setuptools
Successfully installed pip setuptools
Cleaning up...
 ---> 1af6434effa5
Removing intermediate container bb7d99b3532c
Step 8 : CMD ["python2"]
 ---> Running in 56111cc16608
 ---> 9130fa0b17c8
Removing intermediate container 56111cc16608
Successfully built 9130fa0b17c8
$ docker run --rm infosiftr/python:2 pip --version
pip 1.5.6 from /usr/local/lib/python2.7/site-packages (python 2.7)

[tianon]

ping @yosifkit

[yosifkit]

LGTM