CA-142595: Extract update_devs_dict

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
CA-142595: update_devs_dict ignores empty keys

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
CA-142595: Remove redundant check

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
CA-142595: extract INVALID_DEVICE_NAME

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
CA-142595: extract _get_block_device_name

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
CA-142595: Remove comment

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
CA-142595: Cleanup unit tests

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>