layout: Implement reserved block count in percentage

[dagwieers]

We need to implement reserved block count in percentage, rather than fixed sizes, otherwise changing the container (logical volume/partition) size may cause problems because the reserved block count is too high/not proportional to its new size.

This one popped up when doing demo restores on very reduced/tight block devices. And while the container was big enough for storing the data, creating the filesystem failed because the reserved block count was larger than what the container was able to handle.

[jhoekx]

See also SF#3498674, where this is also requested.

[dagwieers]

Ok, I was cleaning the TODO file. So we already knew about this problem :-)

[jhoekx]

Fixed in 062f5a2.