Removed `chdir` ad-hoc implementation.

It is not needed due to implementation in zrt project.
Added script for testing python distribution.

File tests.txt contains all test that could be found under Lib/test/ directory.
It includes every test beginning with `test_` as regrtest.py does. Only explicitly
unsupported modules are exluded (see `status.md`).

3test.sh is simple python script that runs `python -mtest.regrtest test_name`
for every test.

It supposed to be replaced in future with regrtest module itself. just waiting
until `os.listdir()` issue is resolved and some spare time.
Marked some tests from python regression test suite as 'skipped'.

Some tests use features not supported under ZeroVM, such as pipes,
subprocessing. These tests are not supposed to pass, so mark them to be
skipped.

We have platform define as "linux2-zvm" and using this condition to check
if tests should be skipped.

This will make tests pass. Next step is to rewrite some of them. This would 
be done outside python regression test suite.
Updated status file.