avocado.result: Docstring fixes and improvements

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.sysinfo: Improve docstrings

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.utils.misc: Improve docstrings

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.utils.memory: Improve docstrings

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #42 from avocado-framework/more-docstring-improvements

More docstring improvements