PEP 8: cleanup src/kimchi/disks.py

Make this file PEP 8 clean

Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Issue #276: logical pool: a quick fix for the device listing rules, back-end

The current logical pool implementation has some problems. It lists ext4
patitions but in fact partitions with FS should not be listed, because
a dual boot system setup can make use of those unmounted partitions. It
also fails to run lsblk for some devices.

According to the discussion on github issue page[1]. We decide to list
only unused partitions and disks, which means, PV and LV will not be
listed, mounted partitions and partition with FS will not be listed.

When lsblk fails to run on a purticular device, it swallows the error
and return an empty dict.

Some kinds of free block device still can not be listed by the current
quick fix, for this is only a *quick* fix. The following cases are not
covered, they should be improved in future patches.
1. PV that doesn't belong to any VG.
  blkid and lsblk do not provide enough information to detect if a PV
  belongs to an VG.

To get the device path, it uses sysfs uevent file to get the device name and
then assume the device path is /dev/<devname>

This patch also drops the defensive coding style of the current
implementation. Defensive coding is not Pythonic. It makes the code
harder to debug, delay the discovery of code error and makes the main
logic unclear. This patch also extract a function to run and parse
lsblk to avoid repeating similar code.

For a long term solution, backend should just list all block devices,
along with information describing if they are in use. The front end
provides a checkbox "filter in use devices" and let users decide what
they want.

[1] https://github.com/kimchi-project/kimchi/issues/276

Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Signed-off-by: Aline Manera <alinefm@br.ibm.com>
Issue #276, logical pool: a quick fix for the device listing rules, front-end

The current front-end implementation filter out disks from the free
block device listings. This is not needed after the previous back-end
pat correctly listing free disks.

Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>