Proposal: honor root_device also when is a software RAID (bsc#1161331)

[ancorgs]

Problem

In order to support S130/S140/S150 controllers (and also to be more compatible with the old storage), when a software RAID is completely empty (not formatted and not partitioned), it will be considered as a candidate device for the storage proposal.

As proven by #1043, in SLE-15-SP1 that resulted in a proposal that locates the /boot/efi partition inside the software RAID. Although that can be a bit controversial, Dell was happy with this behavior (their S130/S140/S150 controllers has indeed proven to be able to boot the resulting setup) and nobody has complained.

But in TW and in the beta versions of SLE-15-SP2, the proposal tries to locate the /boot/efi partitions directly in one of the physical disks and that leaded to an infinite loop.

Solution

This pull request:

• Merges Test to demostrate bsc#1161331 is not present in SP1 #1043, so we ensure the unit test is also present in master
• Fixes the proposal to place the boot-related partitions in the software RAID, which restores the behavior from SLE-15-SP1

This pull request does NOT include a fix for the infinite loop. The loop cannot longer be triggered in normal circumstances, but there is still a chance for it to reappear in the future. That will be addressed in a separate pull request with much lower priority.

Testing

Merged the mentioned unit test.

[coveralls]

Coverage remained the same at 97.634% when pulling b978817 on ancorgs:bug_1161331 into 1f0b7ba on yast:master.

[dgdavid]

LGTM

[yast-bot]

✔️ Public Jenkins job #266 successfully finished
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[yast-bot]

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