Bring h5diffgentest in line with expected test files

[mattjala]

• Add files to gentest script: trefer_attr.h5, tvlstr.h5, tvlstr2.h5

The routines to build these are copied from h5dumpgentest. It might make sense to eventually have a separate collection of shared build file generator routines that can be shared between gentest scripts.

• Fix cases where the expected datataype does not match the generated one

• Fix some object names not matching their expected values

• Update test files and expected files for test_comps_array_vlen and test_comps_vlen_arry

• Fixed incorrect datasets being compared for compound dataset test

• Update the (disabled for now) h5diffgentest CMake test to create files in the correct directories

We can't just copy the testfiles to the parallel directory because the active VOL connector may not use files.

[byrnHDF]

One thing that is missing and needs to be handled - the tools will need reference files generated if any of the testfiles change.

[mattjala]

One thing that is missing and needs to be handled - the tools will need reference files generated if any of the testfiles change.

None of the testfiles are changed here. The gentest script is out of date and currently creates testfiles that are different than the one we have committed. This is changing gentest to create testfiles identical to the ones we already have.