Separate snapshot definition

Current snapshot definition is located in the CC module, so it is
difficult to capture non-CC module (such as prebuilt_etc) to the
snapshot. Separate general snapshot definition from cc so other modules
can also define its own snapshot.

Bug: 192430376
Test: m nothing passed
Change-Id: Ifb69fb3d2ec555b629aa31ec03e7ce5831fd3063
diff --git a/cc/sdk.go b/cc/sdk.go
index 69ad311..a83e5ad 100644
--- a/cc/sdk.go
+++ b/cc/sdk.go
@@ -76,7 +76,7 @@
 			}
 			ctx.AliasVariation("")
 		}
-	case *snapshot:
+	case *snapshotModule:
 		ctx.CreateVariations("")
 	}
 }