set date_from for calendar during initial load of dialog.

Changed code to set date_from for calendar during initial load of dialog. Removed setting of miq_cal_dateFrom JS variables from dialog_runner that was being done after a field is changed in the form no need to do it there as value of show past dates cannot be changed once dialog is loaded.

https://bugzilla.redhat.com/show_bug.cgi?id=1052795
Merge pull request #727 from h-kataria/disbale_past_dates_when_show_past_dates_is_not_selected

set date_from for calendar during initial load of dialog.