Let genrule have the entrance depend on signapk

Currently, it may be a good idea to let genrule module depend on
java_library_host by changing soong. To change signapk module type from
java_library_host to java_binary_host makes the genrule can depend on the
signapk module directly and generate the signapk.jar at the same time.

Test: for i in `seq 1 10` ; \
        do\
            make clean; \
            make -j64 apexer_test_host_tools; \
        done
Bug: 160632228
Bug: 157878202
Change-Id: I63ae661b9b419ddc6e69ccfc9a29fd28b116c0b5

tools/signapk/Android.bp

@@ -16,7 +16,7 @@
 
 // the signapk tool (a .jar application used to sign packages)
 // ============================================================
-java_library_host {
+java_binary_host {
     name: "signapk",
     srcs: ["src/**/*.java"],
     manifest: "SignApk.mf",
@@ -32,6 +32,7 @@ java_library_host {
     // The post-build signing tools need signapk.jar (and its shared libraries,
     // handled in their own Android.bp files)
     dist: {
+        tag: ".jar",
         targets: ["droidcore"],
     },
 }