Support installable prebuilt jars

Some host modules need to be installed.  Add an installable property.

Test: m checkbuild
Change-Id: Ifd023213ff66e81aa77ba1741c75837a1dd88d1d
diff --git a/java/java.go b/java/java.go
index 497b285..fbd7bdd 100644
--- a/java/java.go
+++ b/java/java.go
@@ -920,6 +920,8 @@
 	Jars []string
 
 	Sdk_version string
+
+	Installable *bool
 }
 
 type Import struct {