Remove agentil_instance type

The current `agentil_instance` type was badly modeled so remove the
type. The instances of a system should really be a parameter of the
`agentil_system` type, instead of a separate resource. But to accomplish
that, the `agentil` utility classes will need some refactoring.

So in the end ability to manage the monitored instances with puppet
will return, but to refactor the code to allow implementing it in a
sane way is easier, if we first remove the type completly.
Add more documentation in restart_probe.sh
Remove usage function from restart_probe.sh

The usage function was only ever called once so we can just inline it.
Refactor agentil util classes

The different agentil classes shared a lot of implementation and there a
deep relationships between the types (e.g. a landscape has assigned
systems and each system has assigned templates etc) but there was not
central registry that had access to all objects.

Create a new class Puppet::Util::Agentil that holds a map of landscapes,
systems, users, and templates and is responsible for adding and removing
instances.
Fix rspec deprecation warnings

Recent versions of rspec raised a deprecation warning of the following
when running the tests:

    `expect(collection_owner).to have(2).landscapes` is deprecated. Use the
    rspec-collection_matchers gem or replace your expectation with something
    like `expect(collection_owner.landscapes.size).to eq(2)` instead.

Use the new version and not the deprecated version to test the number of
elements in a collection.
Remove the agentil job helper class

The agentil job class was formerly used to describe a customized job of
a specific template. This caused more overhead as necessary since every
customized job has completly different values. As a result a template
only stores a hash of customized jobs with the configuration element as
a value and no job object now.

This way a provider can query a specific job-overwrite and has to make
use of the returnes structure on its own.
Add template property tablespace_used

The property tablespace_used can be used to overwrite tablespace
thresholds for job 166 (used tablespace in percent) of the specified
template.
Add template property expected_instances

The expected_instances property can be used to customize job 166
(instance availability) for a specific system template. It takes a
simple array and automatically assumes auto_clear => true, mandatory =>
true, criticality => critical.
Update Readme
Remove registry

There was no use in refering to Puppet::Util::Agentil indirectly so
remove the unnecessary abstraction.
Merge branch 'agentil_tablespace_customthreshold'

* agentil_tablespace_customthreshold:
  Remove registry
  Update Readme
  Add template property expected_instances
  Add template property tablespace_used
  Remove the agentil job helper class
  Fix rspec deprecation warnings
  Refactor agentil util classes
  Remove usage function from restart_probe.sh
  Add more documentation in restart_probe.sh
  Remove agentil_instance type