Allow installd to create the lib symlink for system_app_data_file

91a4f8d4 created system_app_data_file,
and assigned all system_apps to use this file type. For testing purposes,
our automated testing infrastructure sideloads shared system UID apks.
Installd does not have permission to create the lib symlink, so the
installation fails.

Allow installd to create this symlink.

  repro:
  adb install AppLaunch.apk
  276 KB/s (8414 bytes in 0.029s)
         pkg: /data/local/tmp/AppLaunch.apk
  Failure [INSTALL_FAILED_INTERNAL_ERROR]

  logcat:
  05-08 23:16:36.336   605   637 I PackageManager: Copying native libraries to /data/app-lib/vmdl609237490
  05-08 23:16:36.338   605   637 W asset   : Installing empty resources in to table 0x5e89a368
  05-08 23:16:36.359   193   193 W installd: type=1400 audit(0.0:29): avc:  denied  { create } for  name="lib" scontext=u:r:installd:s0 tcontext=u:object_r:system_app_data_file:s0 tclass=lnk_file
  05-08 23:16:36.363   193   193 E installd: couldn't symlink directory '/data/data/com.android.tests.applaunch/lib' -> '/data/app-lib/com.android.tests.applaunch-1': Permission denied
  05-08 23:16:36.364   605   637 W PackageManager: Failed linking native library dir (user=0)
  05-08 23:16:36.364   605   637 W PackageManager: Package couldn't be installed in /data/app/com.android.tests.applaunch-1.apk

Bug: 14659632
Change-Id: Iac4890302cd070aa3f71553af217f343ed7b8bc3

installd.te

@@ -31,6 +31,7 @@ allow installd bluetooth_data_file:lnk_file { create setattr };
 allow installd nfc_data_file:lnk_file { create setattr };
 allow installd radio_data_file:lnk_file { create setattr };
 allow installd shell_data_file:lnk_file { create setattr };
+allow installd system_app_data_file:lnk_file { create setattr };
 # restorecon /data/data
 allow installd unlabeled:dir relabelfrom;
 allow installd unlabeled:notdevfile_class_set relabelfrom;