[SUSE] Fix group ownership for SUSE (openSUSE & SLE)

SUSE systems (openSUSE and SUSE Linux Enterprise) do not create a group
for each user. It uses a general 'users' group.

Without this patch, SUSE users will get an error message like the
following when running `./dev setup-unit-tests`:

````
chown: invalid user: 'jamestyj.jamestyj'
````
[Dev setup] Remove unnecessary requires to reduce setup dependencies

Remove unused requires to reduce the dependencies needed to run
`./dev setup-unit-tests`.
[Dev setup] Add --no-gem-cache option to ./dev setup-unit-tests

For some dev setups there's no need to use a gem cache - they can
directly install gems from rubygems.org. This simplifies and speeds up
the dev setup process.

Usage:

````
./dev setup-unit-tests --no-gem-cache
````
[Dev setup] Add warning about using --no-gem-cache

As requested by Victor during pull request review.
Merge pull request #1665 from jamestyj/jamestyj-setup

[SUSE] Fix group ownership for SUSE (openSUSE & SLE)
Merge pull request #1666 from jamestyj/jamestyj-reduce-setup-dependencies

[Dev setup] Remove unnecessary requires to reduce setup dependencies
[openSUSE] Add docs for setting up an openSUSE dev environment

Now that the Crowbar code is able to run on Ruby 1.9, we can get Crowbar
to run on openSUSE 12.2, which doesn't directly support Ruby 1.8.7 (one
can use `rvm` but we want to avoid adding another layer).

The steps described in the openSUSE guide will only work smoothly when
the following pull requests are merged:

- https://github.com/crowbar/crowbar/pull/1665
- https://github.com/crowbar/crowbar/pull/1666
- https://github.com/crowbar/crowbar/pull/1667
- https://github.com/crowbar/crowbar/pull/1668

Also updated the Ubuntu guide to reflect recent changes and fixes.
Merge pull request #1669 from jamestyj/jamestyj-opensuse

Good for now.  This should move/rename when we have the /doc directory working (a deliverable for this sprint).
Fix links to openSUSE and Ubuntu READMEs

The relative links work when viewing the page from https://github.com/crowbar/crowbar/edit/master/dev-setup/README.md, but not from https://github.com/crowbar/crowbar/tree/master/dev-setup. So just use absolute links instead.
Minor tweak to VM download link
Update outdated links
Oops did not intent to commit in earlier push
Merge pull request #1667 from jamestyj/jamestyj-no-gem-cache

[Dev setup] Add --no-gem-cache option to ./dev setup-unit-tests
To bring the JSON to match the RA
Merge pull request #1670 from rperryman/master-0b75d7de0943b68887543c97725297e5b13c3422

Update to the RA [1/1]
Merge branch 'master' of https://github.com/crowbar/crowbar
barclamp install moves to docs to new location
new home for model_barclamp (instead of crowbar barclamp)
staging moving of documentation
add relationship between attribute and barclamp