trac#308: Fill in TestResult[@version] every time new TestResult gets created.
trac#308: Never export element version to TestResult

Addressing:
OpenSCAP Error: File '/tmp/test_xccdf_multiple_testresults.out.t0OrWR' line 0: Element '{http://checklists.nist.gov/xccdf/1.2}version': This element is not expected. Expected is one of ( {http://checklists.nist.gov/xccdf/1.2}benchmark, {http://checklists.nist.gov/xccdf/1.2}tailoring-file, {http://checklists.nist.gov/xccdf/1.2}title, {http://checklists.nist.gov/xccdf/1.2}remark, {http://checklists.nist.gov/xccdf/1.2}organization, {http://checklists.nist.gov/xccdf/1.2}identity, {http://checklists.nist.gov/xccdf/1.2}profile, {http://checklists.nist.gov/xccdf/1.2}target ).
trac#308: export TestResult[@version]