Hide the paging controls in Chargeback -> Assignments -> Storage

The call to the 'cb_rates_list' method applies to the Rates accordion
only and should not be called in explorer since that fetches the
chargeback rates list and displays a paging control at the bottom of
the 'Assignments' page where the paging controls are not applicable.

https://bugzilla.redhat.com/show_bug.cgi?id=1166187
Fix File.exists? deprecation warning

rubocop -a --only Lint/DeprecatedClassMethods
http://www.refactorcop.com/manageiq/manageiq
Replace File.exists? with File.exist?
Fix test stub/expectations to use File.exist? instead of File.exists?.
Merge pull request #1111 from jrafanie/fix_file_exist_deprecation

Fix File.exists? deprecation warning
Fix race condition in smart proxy.

Ignore EEXIST error if directory is created by another thread after existence check.

https://bugzilla.redhat.com/show_bug.cgi?id=1148971
https://bugzilla.redhat.com/show_bug.cgi?id=1153784
Merge pull request #1113 from roliveri/smart_proxy_race_condition

Fix race condition in smart proxy.
Merge pull request #1109 from AparnaKarve/bz1166187_dont_display_pagecontrols_in_assignments

Hide the paging controls in Chargeback -> Assignments -> Storage