It has been reported that avocado crashes when a malformed command
is attempted to be executed, even when using `shell=True`.

The reason is that `shlex.split` will raise `ValueError` on those
commands. Since improving `shlex.split` may be too complex, and
possibly not the best place to "fix" this, let's just assume safely
that this command should be run on GDB.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

To be honest, our test code could still be kept in the same directories and
have the same names. But I think we can improve two things here:

1) Flatten a little bit the directory structure of selftests. Two path
components are being dropped here: "all" and "avocado". So that
"selftests/all/functional/avocado" becomes simply
"selftests/functional".

2) File names match what is, by default, recognized by unittest (the
Standard Library module) based discovery of tests. That means that
doc_build_test.py becomes test_doc_build.py. Not a big deal IMHO.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

Instead of having a "common ground" that two namespaces would import and
share runtime information, let's just make the plugin set the defaults
for the module.

This is quite appropriate, both regarding the namespace where the
configurations are kept (in the avocado.utils.gdb module itself) and
also regarding the single direction of module layering.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

Self test files used to be executable, but that changed on 143b574c.
So, it doesn't make much sense to keep the shebangs + python commands
on them.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

So that any code using our process API can be run through a debugger.
Signed-off-by: NCleber Rosa <crosa@redhat.com>