Separate system_version and product_version.

system_version will be at /etc/os-release.d/system_version, no symlink.
product_version still at oem partition, but now has only one number.

Bug: 35364984
Test: m droid dist oem_image custom_images -j
Change-Id: If0f357d29c8dd0cec1ff4999a3c42b0362a45c01
(cherry picked from commit 9b173cccb8bdb750d4cf7855e5379ceee5ba030f)
1 file changed