blackbox: Update README, add --homedir to encryption step in _blackbox_common
blackbox: Removed homedir and updated README to add step to import pubring
blackbox: Removed the manual gpg --import step from README, added prepare_keychain to blackbox_update_all_files
Merge pull request #20 from loadstar81/master

Add a call to prepare_keychain in blackbox_update_all_files
Merge pull request #17 from christophebiocca/fix-python

Puts parens in print call, for python3 compatibility.
Merge pull request #19 from christophebiocca/umask

Uses umask to avoid creating world-readable files.
Run commands in an unencrypted tmp copy.