releasetools: Conditionally apply lzma compressor

LZMA_RAMDISK_TARGETS only affects generated images stored in
out/target/product/<x>/ at the moment, but not those which are
generated when an OTA package is built.

Fix this behavior so devices that expect to have their ramdisks
compressed can apply OTAs without breakage because of images being
too large.

Change-Id: Iab17215115c7b4887eac54f7bfbcd37444850ac7
Signed-off-by: Christopher N. Hesse <raymanfx@gmail.com>