Populate BRILLO_CRASH_SERVER from the product config

Using cfgtree.mk, this change adds support to load the
crash server URL directly from a file in the product tree
during the build.

BUG=25343470
TEST=build image, check in etc for the populated osrelease.d file

Change-Id: I6342a829936809b9553a32be7bc58285c86dd732
1 file changed