avocado.virt.qemu.devices: Use Borg class from avocado base APIs

Due to its utility, the Borg class was moved to avocado.utils.data_structures
module. Let's get rid of the local copy in devices.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.virt: Mass PEP8 Fix

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.virt.qemu.devices: Change docstring style, clarify some choices

Change the docstring style in that file to be more similar
to the style used in other files. Also, add a little bit
of explanation on why we call 'parts of the QEMU command line'
'devices'.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.virt.qemu.devices: Remove unused parameter from add_nodefaults

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.virt.qemu.devices: Remove short intermediary method

Given the simplicity of the method, we might as well omit
the intermediary method.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado.virt.qemu.devices: Simplify .add_vnc() method

There's really no need to use .port as a class attribute
(it's too generic), so let's remove it from the class
and keep using a method internal variable.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #26 from lmr/use-borg-from-avocado-plus-fixes

Use borg from avocado plus fixes