Remove dead code

yum_install has been superseded by omnibus installer.
Move Linux specific bootstrap methods to appropriate subclass
Rename debian_gem_install to debianoid_gem_install for consistency
Remove obsolete :version attribute from bootstrap distro types
Make sure "ca-certificates" package is installed on Debian

Minimal Debian build does not include CA certificates and thus
downloading the omnibus installer with https fails.
Upgrade the Debian squeeze AMI to Debian 6.0.7

The new AMI does not include curl nor ca-certificates, so this also
tests the previous commit.
Merge pull request #213 from tmatilai/debian-ca-certificates

Make sure "ca-certificates" package is installed on Debian