Pulp

Description of problem:
builder.py seems to be using a feature that was new in Python 2.7:

$ ./builder.py --update-tag-package-list 2.4 beta
Traceback (most recent call last):
File "./builder.py", line 531, in <module>
add_packages_to_tag(build_tag)
File "./builder.py", line 482, in add_packages_to_tag
result = str(subprocess.check_output(command, shell=True))
AttributeError: 'module' object has no attribute 'check_output'

Version-Release number of selected component (if applicable):
2.4.1-0.2.alpha

How reproducible:
very

Steps to Reproduce:
1. ./builder.py --update-tag-package-list 2.4 beta

Actual results:
Traceback!

Expected results:
Tags should have been updated.

Additional info:

+ This bug was cloned from Bugzilla Bug #1133146 +