Don't format chargeback rate column in MiqReport::Formatting

[lpichler]

This is not best fix but usable for backport

Issue:
Some of "float" format was taken for chargeback rate columns which are strings.
Solution is to don't format such columns

[----] E, [2018-11-01T11:25:45.469900 #11829:93af80] ERROR -- : /opt/rh/cfme-gemset/bundler/gems/cfme-ui-classic-75b755f67a94/app/helpers/number_helper.rb:53:in `Float'
/opt/rh/cfme-gemset/bundler/gems/cfme-ui-classic-75b755f67a94/app/helpers/number_helper.rb:53:in `handling_negatives'
/opt/rh/cfme-gemset/bundler/gems/cfme-ui-classic-75b755f67a94/app/helpers/number_helper.rb:4:in `number_to_human_size'
/var/www/miq/vmdb/app/models/miq_report/formatting.rb:122:in `format_bytes_to_human_size'
/var/www/miq/vmdb/app/models/miq_report/formatting.rb:90:in `apply_format_function'
/var/www/miq/vmdb/app/models/miq_report/formatting.rb:75:in `format'

Links

• https://bugzilla.redhat.com/show_bug.cgi?id=1645193

@miq-bot assign @gtanzillo
@miq-bot add_label hammer/yes, bug, chargeback

[miq-bot]

Checked commit lpichler@bad74a9 with ruby 2.3.3, rubocop 0.52.1, haml-lint 0.20.0, and yamllint 1.10.0
2 files checked, 0 offenses detected
Everything looks fine. ⭐

[gtanzillo]

LGTM 👍