Merge config to knife classes instead of overwriting it

Maintain possible default values.
Install misc rpm packeges before chef

Be consistent with other *_install methods.
Also remove obvious comments.
Drop support for openSUSE 11

Omnibus installer only supports openSUSE 12.
Ensure rsync is installed on openSUSE

For example the 12.2 AMIs offered by SUSE Studio do not have rsync
installed. (We can not add integration test for them as Omnibus
install.sh does not support 12.2 even though the package for 12.1
works fine.)
Merge branch 'opensuse'
Sort development dependencies in gemspec
Remove hard dependency on Librarian-Chef

Only try to use the librarian gem if the Cheffile is found (and
`--no-librarian` is not specified). Complain to the user with
instructions if the gem is not found.

Also add a debug message is the Cheffile is not found.
Fix typo in `--omnibus_version` descriptions

[ci-skip]
Add unit tests for librarian gem detection
Try to load Librarian dependencies only if really needed
Lock down librarian dev dependency to v0.0.x

librarian v0.1.0 will not include librarian-chef any more,
as it will be extracted to own gem.
Clean up warning message of Librarian-Chef absence
Use `FileUtils.touch` to create empty Cheffiles on tests
Add helper for accessing options in correct precedence

Add a Chef 10 compatible way of getting correct precedence for command line
and configuration file options. Adds correct handling of `false` values
to the original example in
http://docs.opscode.com/breaking_changes_chef_11.html#knife-configuration-parameter-changes
Fix :librarian configuration handling

Librarian-Chef was not run by default when SoloCook/Bootstrap was
invoked by for example `knife bootstrap --solo` (from #207) or `knife
digital_ocean droplet create --solo` (from knife-digital_ocean).

The reason is that the `Knife.config` is not loaded by default values
when the Knife class is initialized. While this could be fixed in
the invoking code it is much cleaner to do moving the default value
setting to later in the code.

As an extra bonus, by using our `config_value` helper we also make it
possible to use `knife[:librarian]` configuration option with Chef 10,
too.
Merge pull request #211 from tmatilai/librarian-dependency

Remove hard dependency on librarian
Update changelog
Merge pull request #221 from tmatilai/librarian-option

Librarian-Chef is not run by default when SoloCook/Bootstrap invoked from ruby
Add also a module method for `Tools#config_value`

This way we don't need to include the Tools module to use
the helper.
Add #221 to the changelog