Add Google Cloud Engine (GCE) provider:

 * force kpartx to use synchronous mode, removing sleep(10)
 * get image configuration, use it during tarball creation and registration
 * add (non-working, path problems) image registration
 * add cleaning of image from Google keys and repositories
 * add NTP server address in manifest
 * add preference for backport kernels in manifest
 * disable IPv6
 * correctly set host name
Merge pull request #80 from rybaktomasz/gce_development

Add Google Cloud Engine (GCE) provider:
Fix import error with cloud_init task
Fixes #14 and #78
S3 images can now be bootstrapped outside EC2.
However, this fix adds the requirement of a "region" setting.
At some point we could make "region" optional and fail when bootstrap-vz
is run outside EC2 and no "region" is set.
Require hostname setting for vagrant plugin
Also, fix reference to vbox src to a revision
Simplify adding tasks
There is now a get_standard_groups function
Add ssh_group, which configures SSH properly
Remove unused imports
Create security group (part of standard group)
Don't add initd installation task in vbox provider
Add get_standard_rollback_tasks()
This simplifies the the providser rollback_tasks fn considerably
Generalize "grub only on partitioned volumes" err
(move it into base manifest validation)
Add stuff to changelog
Fix import errors, again.
(A rebase swallowed a commit somewhere)
Add multiple threads to log_call

Conflicts:
	bootstrapvz/common/tools.py
Add a test for log_call.
Make log_call a little shorter as well, stream_readline() is now a closure.