Since the LVM support was added to all distros, our disk
related code is adaptive, i.e. we will set the correct BLS
and grub2 prefix if there a `boot` partiton is present in
the layout after all customizations happen, which includes
LVMification.
One thing that was not yet fully working was layouts that
do not yet have a `/boot` partition but allow LVMification.
In that case `NewPartitionTable` and if `/boot` was the
first (or only) customization, would LVMify the partition
which in turn would create the `/boot` partition; but after
`newPT.ensureLVM()` the call to `newPT.createFilesystem`
with `/boot` would try to create another `/boot` mountpoint.
In order to deal with this situation correctly we are now
using a two phase approach: 1) enlarge existing mountpoints
and collect new ones. 2) if there are new ones and LMVify
was allowed, switch to LVM layout. Do a second pass and now
create or enlarge existing partitions, handling `/boot` in
the process.
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