Allow for overriding container packagename for an Apex.

Test: go test ./... -test.v -run TestOverrideApex
BUG: 148198056
Change-Id: If49042a7acbf9f0dcb505664863d97805902e459

apex/builder.go

@@ -657,6 +657,9 @@ func (a *apexBundle) getOverrideManifestPackageName(ctx android.ModuleContext) s
 		}
 		return ""
 	}
+	if a.overridableProperties.Package_name != "" {
+		return a.overridableProperties.Package_name
+	}
 	manifestPackageName, overridden := ctx.DeviceConfig().OverrideManifestPackageNameFor(ctx.ModuleName())
 	if overridden {
 		return manifestPackageName