[openvz] Fixes #1871 test helper callback

This moves the setting up of an `at_exit` callback from when the file
is required to when the matching helper is used.

This prevents it failing on any run where OpenVZ is excluded.
Fix autoincrement when creating a flavor if private flavors exist.

Before, only public flavors were considered when finding the next free ID. That could lead to the case where the calculated ID was already taken which lead to a conflict. This happened whenever the user tried to create a private flavor via fog and then another (private OR public) flavor afterwards. Now, we also take private flavors into account, so the conflict cannot happen anymore.

As a side effect, it is now also possible to just return all private flavors, using the :is_public => false filter on the list_flavors_detail API call or the flavors collection.
[rackspace|dns] fixing DNS pagination issue #1887
Add SimpleCov and Coveralls.io dependenices
Add rake tasks for travis, which include publishing coverage reports.
Change travis to use a rake task instead of shindont directly.
This is partly necessary for
https://github.com/lemurheavy/coveralls-ruby/pull/20, though
I'm a fan of running just "rake" or "rake travis" for simplicity
anyways.
The actual simplecov/coveralls setup.
The use of Process.pid is an attempt to avoid confusing SimpleCov when
running tests in parallel.  Other tests frameworks take a similar
approach when they detect parallel_tests.
[rackspace|dns] added total_entries attribute to zones
[rackspace|dns] adding :limit => 100 to clarify that all returns a limit of 100 records per page at @rupakg suggestion.
[digitalocean] Rename do to docean in examples

Avoids using a reserved word, and `docean` is also used elsewhere in
the getting started guide.
Initial documentation for using Fog with CloudSigma.
Fixed typos.
Update excon dependency to version ~>0.25.0
[vsphere] fix regex typo
[Brightbox] Updates to add collaborations

Adds requests and models for collaborations
[Brightbox] Extract Compute::Shared to own file

Seeing a lot of churn in lib/fog/brightbox/compute.rb because of adding
new requests or models as well as any implementation changes.

This moves the common behaviour between Compute's Real and Mock
classes into their own file to cut down on the noise when refactoring or
merging.
Some cleanup based on comments on the PR