Better relationship matcher descriptions

The current description for the relationship matchers is not very descriptive

```
  should contain Package[foo]
```

The new description 

```
  should contain Package[foo] that comes before File[/etc/foo.conf]
```

Also the relationship can have an array argument to test for relationships with multiple resources.

```ruby
  it { should contain_package('foo').that_comes_before(['File[/etc/foo.conf]','File[/etc/foo.conf.d]']) }
```

```
  should contain Package[foo] that comes before File[/etc/foo.conf] and File[/etc/foo.conf.d]
```