Updated python-pip packages fix security vulnerabilities

Updated python-pip and python-virtualenv packages fix security vulnerability: The mirroring support in python-pip was implemented without any sort of authenticity checks and is downloaded over plaintext HTTP. Further more by default it will dynamically discover the list of available mirrors by querying a DNS entry and extrapolating from that data. It does not attempt to use any sort of method of securing this querying of the DNS like DNSSEC. Software packages are downloaded over these insecure links, unpacked, and then typically the setup.py python file inside of them is executed (CVE-2013-5123). This was fixed in python-pip by removing the mirroring support (i.e., the --use-mirrors, -M, and --mirrors flags). With the updated version, in order to use a mirror, one must specify it as the primary index with -i or --index-url, or as an additional index with --extra-index-url. The python-virtualenv package bundles a copy of python-pip, so it has also been updated to fix this issue. The python-virtualenv package bundles python-requests as well, so this update fixes the session fixation issue CVE-2015-2296 in the bundled python-requests.