init: filter .##rc with preview SDK version

On a preview device (where codename is not "REL"), filtering .##rc files
will choose the highest versions reglardless of ro.build.version.sdk.

Bug: n/a
Test: add .36rc to an apex and see if init reads it.
Change-Id: Icd63cf70e45cc14504f839ce9492e1766147a40e