Don't use interpolation in gettext strings

[mzazrivec]

Fixes the following CI failure:

 1) placeholders gettext strings do not contain interpolations
     Failure/Error: expect(errors).to be_empty
       expected `["\"Cancel operation is not supported for \#{self.class.name}\""].empty?` to return true, got false
     Shared Example Group: :placeholders called from ./spec/i18n/placeholders_spec.rb:2
     # ./spec/shared/i18n/placeholders.rb:49:in `block (2 levels) in <top (required)>'

@miq-bot add_label internationalization, hammer/yes

[mzazrivec]

@simaishi Could you please cherry-pick this one into hammer so that I can rebase #18040 ? Thanks.

[simaishi]

Hammer backport details:

$ git log -1
commit 5981f28e81c13525e14fbb03311d8b1537645017
Author: Nick Carboni <[email protected]>
Date:   Mon Oct 8 09:06:00 2018 -0400

    Merge pull request #18067 from mzazrivec/dont_use_interpolations_in_gettext
    
    Don't use interpolation in gettext strings
    
    (cherry picked from commit 1db6992b5076a99e13623c3de8df5030077ab341)