Combine compress and save image into one function

When compressing an image, this is done in the same dir where the raw
image resides, doubling the amount of space needed (scarce when
using tmpfs), and then it's moved to the .cache folder in disk.

Combining these two functions, we reduce the amount of space needed
in the tmpfs partition (when in use), and the compressed image is
created directly on the .cache folder disk, so there is no need to
move the compressed image after the process into disk.

Change-Id: I451d24bdd6fa0983414244135dff5e96c0549833
Merge "Combine compress and save image into one function"