Add support for specifying the android.jar to link against

In order to run this tool outside of the build system we need to be
able to use something other than a hardcoded location for the current
sdks android.jar.

Test: m com.android.runtime.debug
Bug: 119332365
Bug: 119332362
Change-Id: I8f7f3cc39a91e96b4de727e906f253ba451f7806
diff --git a/apexer/apexer.py b/apexer/apexer.py
index ba5a8f0..fc580bc 100644
--- a/apexer/apexer.py
+++ b/apexer/apexer.py
@@ -80,6 +80,9 @@
                       help='type of APEX payload being built "zip" or "image"')
   parser.add_argument('--override_apk_package_name', required=False,
                       help='package name of the APK container. Default is the apex name in --manifest.')
+  parser.add_argument('--android_jar_path', required=False,
+                      default="prebuilts/sdk/current/public/android.jar",
+                      help='path to use as the source of the android API.')
   return parser.parse_args(argv)
 
 def FindBinaryPath(binary):
@@ -361,7 +364,7 @@
   # specified in AndroidManifest.xml
   cmd.extend(['--version-code', str(manifest_apex.version)])
   cmd.extend(['-o', apk_file])
-  cmd.extend(['-I', "prebuilts/sdk/current/public/android.jar"])
+  cmd.extend(['-I', args.android_jar_path])
   RunCommand(cmd, args.verbose)
 
   zip_file = os.path.join(work_dir, 'apex.zip')