Define getSnapshotNameSuffix()

By sharing a single function for generating snapshot name suffix,
make sure both the DepsMutator and the snapshot modules use the same
names.

Bug: 179666286
Test: m nothing
Change-Id: I9efa94f2981a6bd1b4128bf0e84ca44873ebf3b7
diff --git a/cc/vendor_snapshot_test.go b/cc/vendor_snapshot_test.go
index 4b76f51..0833277 100644
--- a/cc/vendor_snapshot_test.go
+++ b/cc/vendor_snapshot_test.go
@@ -421,6 +421,7 @@
 		shared_libs: [
 			"libvendor_without_snapshot",
 			"libvendor_available",
+			"libvndk",
 		],
 		arch: {
 			arm64: {