Add disk space check.

gcimagebundle now checks disk free space.  If there is not enough free disk space,
it will abort before copying the files. Currently, the disk space calculation
overestimates the space required.  The user can use --skip_disk_space_check to
disable the disk space check.
Add pauses back to gcimagebundle.
Fixes authorized_keys file permissions

Owner and group id are not inherit when calling shutil move. This commit
moves setting permissions logic for the authorized_keys file to be sure
that the final destination file has the proper permissions.
Merge pull request #47 from jeremyje/master

Add pauses back to gcimagebundle.
Merge pull request #45 from yueluog/master

Add disk space check.
fixes #48, account manager was not starting on upstart systems
support both CentOS and Debian derivatives
Merge pull request #49 from erjohnso/master

fixes #48, account manager was not starting on upstart systems
Merge pull request #46 from frodenas/master

Fixes authorized_keys file permissions