Description of problem:
When I clone recipe with following hostrequires:

<hostRequires force="dell-per820-02.khw.lab.eng.bos.redhat.com">
  <and>
    <arch op="=" value="x86_64"/>
    <cpu_count op="&gt;" value="1"/>
    <hypervisor op="=" value=""/>
  </and>
  <system_type value="Machine"/>
</hostRequires>

Beaker complains with this error message:

Job failed schema validation. Please confirm that you want to submit it.
    Line 21, col 0: Invalid attribute force for element hostRequires
    Line 6, col 0: Invalid sequence in interleave
    Line 6, col 0: Element recipe failed to validate content
    Line 5, col 0: Element recipeSet failed to validate content

but according to beaker-job.rng "force" attribute should be allowed:
      <element name="hostRequires">
        <a:documentation xml:lang="en">
          This element is a container for expressing constraints on the
          system which will be selected to run this recipe.
        </a:documentation>
        <choice>
          <attribute name="force">
            <data type="string"/>
            <a:documentation xml:lang="en">
            Select a specific system by FQDN. This bypasses the
            normal filtering mechanisms for selecting a system,
            and always uses the named system regardless of its
            current condition. No other filter criteria can be
            specified when this attribute is used.
            </a:documentation>
          </attribute>

Version-Release number of selected component (if applicable):
21.2

How reproducible:
always

Steps to Reproduce:
1. try to clone recipe with hostrequires that has "force" attribute

Actual results:
Beaker validation error

Expected results:
clone should work without errors

Additional info: