Avoid direct float comparisons with 0.0 in storage.rb

[djberg96]

Currently the rubocop linter gives us a handful of warnings for the Storage class like this:

app/models/storage.rb:621:5: W: Lint/FloatComparison: Avoid (in)equality comparisons of floats as they are unreliable. used_space.to_f == 0.0 ? 0.0 : (debris_size.to_f / used_space.to_f * 1000.0).round / 10.0

So, this PR just switches them to use the zero? method. Core Ruby appears to have its own code for checking floats vs. zero (which the zero? method uses):

https://github.com/ruby/ruby/blob/master/numeric.c#L1122-L1126

If we feel this isn't worthwhile, then I would vote to update our rubocop config to exclude these.

Update: originally I was only fixing the linter warnings, but I also went ahead and fixed the Style/FloatDivision warnings as well while I was here.

[agrare]

Do we need to cast total_space.to_f if we're just going to check for .zero? ? Wonder if total_space.zero? ? 0.0 : (used_space.to_f / total_space * 1000.0).round / 10.0 would be cleaner

[djberg96]

Agreed, updated.

[miq-bot]

Checked commits https://github.com/djberg96/manageiq/compare/a950a904541618be3be24d9cff83b18831fc99cd~...1b76d191843d09ae8df9715343150a1ccea6ca31 with ruby 2.6.3, rubocop 0.82.0, haml-lint 0.35.0, and yamllint
1 file checked, 0 offenses detected
Everything looks fine. 🍰

[skateman]

Yeah, this broke CI on ui-classic:

  1) StorageController report_data for selected StorageCluster returns associated Storages
     Failure/Error: view.paged_view_search(session[:paged_view_search_options])
     
     NoMethodError:
       undefined method `zero?' for nil:NilClass
     # /home/skateman/Repositories/ManageIQ/manageiq/app/models/storage.rb:589:in `free_space_percent_of_total'

Apparently total_space can be nil