Support gzipped images found in partitions

[valerierx]

When trying to run rmtfs on Motorola surnia, I get the following error: [RMTFS] open [RMTFS storage] request for unknown partition '/boot/modem_fsg/surnia_emea_4', rejecting

Turns out the surnia_emea_4 partition in question is located in the modem_fsg partition as a gzipped image file, along with other images. The current method to satisfy rmtfs is to extract the image, patch the partition table accordingly and move the image to /dev/disk/by-partlabel/