avocado.test: PEP8 fixes

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.sysinfo: Functional SysInfo class

This allows for collecting system information at different
moments of a test run process.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.sysinfo: Create a 'sysinfo' subdir when no basedir provided

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