Remove unneeded use of request.POST

The resource class creation step CreateRacks used to reach directly to
request.POST to get the values of checkboxes. Since using
FormsetTableData, this is no longer necessary or desirable and should
have been cleaned together with introducing FormsetTableData.

Change-Id: I06183116878b001854ffc3995ae914ed9ab2c063
Merge "Remove unneeded use of request.POST"