os-release.d: set the default version to four numbers.

We will report system_version and product_version separately to Omaha,
so revert back to using four numbers for version.

Test: cat $OUT/system/etc/os-release.d/system_version
Change-Id: Ife69a7a17d1a06cc9127540cb39f27ce4fd0c944
(cherry picked from commit d454042d764713ead2b87b78f4d2292d2d422d45)
1 file changed