install kernel & python-software-properties separately

The bootstrap script was installing software-properties-common.
The package which contains add-apt-repository is:
python-software-properties

$ apt-file search add-apt-repository
python-software-properties: /usr/bin/add-apt-repository

The kernel failed to install for me in vagrant, so that step should be
done separately to not break the install. The system might already have
a kernel which is fully docker compatible.
add curl to the list of packages to be installed
Added myself to AUTHORS
Merge pull request #21 from unclejack/fix_bootstrap_script

Fix bootstrap script
bumped buildstep submodule dependency to latest master
installs docker 0.4.2 instead of the latest available
Merge pull request #37 from fcoury/bootstrapping

Bootstrapping improvements
Merge pull request #34 from silasb/add-my-self-to-authors

Added myself to AUTHORS
enables server_names_hash_bucket_size in nginx
added myself to AUTHORS
Merge pull request #38 from fcoury/nginx_config

Enables nginx configuration server_names_hash_bucket_size
replacing ruby json parsing
dropping ruby dependency and cleaning up a simple if statement
Making docker automatically restart previously running containers
Merge pull request #41 from rnorth/auto_restart

Making docker automatically restart previously running containers
Run as superuser where appropriate, and fix up an example.

Pull request #25 introduced pulling the repositories as a normal user
and using sudo to esclate when necessary. This commit fixes broken
examples by adding sudo to the commands that will not work with limited
privileges. This commit also adds ./ to an example where needed.
Merge pull request #42 from rhy-jot/master

Run as superuser where appropriate, and fix up an example
travis ci experiment
Merge branch 'master' of https://github.com/progrium/dokku
will travis like this?