Fix Fedora ignition script.

Fedora ignition script writes image to mmc then attempts to resize p3 of the downloaded image to fill the entire mmc device.  It fails because the author makes the assumption that fdisk will suggest the same start address for the replacement as the original partition.  In the case on the live server, it does not.  When this is the case, the subsequent e2fs operations error out.

To correct the deficiency I added one line of code to record the start address of the last partition on the newly imaged mmc and modified one line to use to use the partition # and start sector of that partition.