Merge branch 'jbolz_pipeline_barrier_fixes2' into 'master'

Merge branch 'jbolz_pipeline_barrier_fixes2' into 'master'

pipeline_barrier: Keep the VkBuffer in the PrepareContext alive until the work is executed...

…, by putting it in the same scope as the execution. Also wait for idle before the destructors are called.

This may not be the best fix, but it works. Buffers can be created and destroyed by various OPs in the test, but I think all the Execute work happens with the last buffer. The test may need some restructuring to using the different buffers.

See merge request !230