Cleanup tests for ptrace() and increase the coverage.

[metan-ucw]

First of all we do have a few tests that needs to be cleaned up and converted to the new test library, once that is done we should look for a missing coverage. The system call is very complex and we have a few tests, so I'm pretty sure that we cover only small part of it.

[coolgw]

https://patchwork.ozlabs.org/project/ltp/patch/[email protected]/ https://patchwork.ozlabs.org/project/ltp/patch/[email protected]/

[coolgw]

Will continue work on it and send new updated patch.