gpt-auto symlinks: take factory reset mode into consideration

gpt-auto symlinks: take factory reset mode into consideration

In relevant factory reset situation the root disk itself is subject to
removal. This somewhat conflicts with automatic root disk discovery,
since the system first comes up with one candidate for the root disk,
which is then replaced by another.

Let's address this by determining at the moment of probing for the
gpt-root logic what the factory reset state currently is. This is then
used to maintain two distinct symlinks to the gpt auto root device: one
which is always available and one that is only available if factory
reset is off or complete.

The new symlinks is not used by anything yet. This will be added in a
later commit.