Split off the entry point for xccdf-report to a separate file

This will help contain all the ARF vs XCCDF 1.1 vs XCCDF 1.2 negotiating
logic. xccdf-report-impl will get all the elements as parameters.
Allow selection of Benchmark ID in the same way TestResult ID is selected

This means that HTML report can be generated from Result DataStream
since this commit. (and the crowd goes wild!)

Both TestResult ID and Benchmark ID are autodetected when not supplied.
The ns_workaround now changes XCCDF 1.1 to 1.2 instead of the other way around
If TestResult doesn't supply the benchmark/@id, try to use root Benchmark

This is mostly for backwards compatibility, openscap always references
the benchmark in TestResult nowadays.
HTML report tests reflect that the new stylesheet is for XCCDF 1.2
security-guide.xsl was renamed to xccdf-guide.xsl