Refactor suggest_single_disk_layout()

[codefiles]

• Simplify home partition conditional and use less indentation
• Simplify root length conditional by de-duplicating repeated home partition conditional checks
• Only call process_root_partition_size() when it is required
• Rename process_root_partition_size() parameter available_space -> total_size for increased clarity
• Consolidate accounting of end alignment buffer

Bonus: -3 lines

[codefiles]

I have more refactors like this for various functions. I am unsure if I should submit pull request for them. Would they possibly be considered too minor and therefore unhelpful?

[svartkanin]

I think any refactoring that improves the code quality and readability is welcome

[codefiles]

Great. Thanks.