Speed up unpack_file_url

by ignoring .tox, .git, .hg, .bzr, and .svn  when doing
`shutil.copytree` in unpack_file_url in pip/download.py.

Fixes: GH-2195
Merge pull request #2196 from msabramo/speed_up_unpack_file_url

Speed up unpack_file_url