[build/setup.sh] Fix install permissions when the host has umask 0077
[build/setup.sh] Fix install permissions when the host has umask 0077

Test Plan:
- Add "umask 0077" to my .bashrc
- vagrant destroy
- vagrant up --provision
- Check the permissions of
  /usr/local/lib/python2.7/dist-packages/pip-1.5.6.egg-info/entry_points.txt
  inside the VM.  It should be world-readable.

Reviewers: siro

Reviewed by: siro

PriviPK/privipk-sync-engine,wakermahmud/sync-engine,gale320/sync-engine,gale320/sync-engine,PriviPK/privipk-sync-engine,closeio/nylas,EthanBlackburn/sync-engine,Eagles2F/sync-engine,PriviPK/privipk-sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,nylas/sync-engine,EthanBlackburn/sync-engine,gale320/sync-engine,jobscore/sync-engine,EthanBlackburn/sync-engine,ErinCall/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,jobscore/sync-engine,wakermahmud/sync-engine,ErinCall/sync-engine,nylas/sync-engine,ErinCall/sync-engine,wakermahmud/sync-engine,EthanBlackburn/sync-engine,Eagles2F/sync-engine,closeio/nylas,PriviPK/privipk-sync-engine,wakermahmud/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,closeio/nylas,closeio/nylas,PriviPK/privipk-sync-engine,gale320/sync-engine,EthanBlackburn/sync-engine,nylas/sync-engine,jobscore/sync-engine,nylas/sync-engine,gale320/sync-engine,jobscore/sync-engine