Fix failing unit tests

Fixes the following unit test failures on Ruby 1.9.3:

```
 1) Error:
    test_deployment_creates_new_if_none_given_and_multiple_allowed(AttribHasDeploymentTest):
    ArgumentError: assertion message must be String or Proc, but Array was given.
    /home/travis/build/crowbar/travis-ci-crowbar/crowbar_framework/test/unit/attrib_has_deployment_test.rb:85:in `block in <class:AttribHasDeploymentTest>'

 2) Error:
    test_deployment_finds_first_if_none_given_and_only_1_allowed(AttribHasDeploymentTest):
    ArgumentError: assertion message must be String or Proc, but Array was given.
    /home/travis/build/crowbar/travis-ci-crowbar/crowbar_framework/test/unit/attrib_has_deployment_test.rb:75:in `block in <class:AttribHasDeploymentTest>'

 3) Error:
    test_deployment_finds_match_if_given(AttribHasDeploymentTest):
    ArgumentError: assertion message must be String or Proc, but Array was given.
    /home/travis/build/crowbar/travis-ci-crowbar/crowbar_framework/test/unit/attrib_has_deployment_test.rb:94:in `block in <class:AttribHasDeploymentTest>'

 4) Error:
    test_deployment_is_created_if_missing(AttribHasDeploymentTest):
    ArgumentError: assertion message must be String or Proc, but Array was given.
    /home/travis/build/crowbar/travis-ci-crowbar/crowbar_framework/test/unit/attrib_has_deployment_test.rb:65:in `block in <class:AttribHasDeploymentTest>'
```

Which then in turns reveals the following actual failing tests:

```
  1) Failure:
     test_deployment_finds_first_if_none_given_and_only_1_allowed(AttribHasDeploymentTest) [/tmp/crowbar-dev-test/opt/dell/crowbar_framework/test/unit/attrib_has_deployment_test.rb:77]:
     <1> expected but was
     <2>.

  2) Failure:
     test_deployment_is_created_if_missing(AttribHasDeploymentTest) [/tmp/crowbar-dev-test/opt/dell/crowbar_framework/test/unit/attrib_has_deployment_test.rb:67]:
     <1> expected but was
     <0>.
```

https://travis-ci.org/crowbar/travis-ci-crowbar/jobs/5495043