Get rid of separate platform_app_data_file type.

The original concept was to allow separation between /data/data/<pkgdir>
files of "platform" apps (signed by one of the four build keys) and
untrusted apps.  But we had to allow read/write to support passing of
open files via Binder or local socket for compatibilty, and it seems
that direct open by pathname is in fact used in Android as well,
only passing the pathname via Binder or local socket.  So there is no
real benefit to keeping it as a separate type.

Retain a type alias for platform_app_data_file to app_data_file until
restorecon /data/data support is in place to provide compatibility.

Change-Id: Ic15066f48765322ad40500b2ba2801bb3ced5489
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Adding permissions needed to remove cache

During removing cache data using Zipper application, I found violation logs.

avc:  denied  { write } for  pid=198 comm="installd" name="cache" dev="mmcblk0p29" ino=81680 scontext=u:r:installd:s0 tcontext=u:object_r:download_file:s0 tclass=dir
avc:  denied  { remove_name } for  pid=198 comm="installd" name="downloadfile.apk" dev="mmcblk0p29" ino=82247 scontext=u:r:installd:s0 tcontext=u:object_r:download_file:s0 tclass=dir
avc:  denied  { unlink } for  pid=198 comm="installd" name="downloadfile.apk" dev="mmcblk0p29" ino=82247 scontext=u:r:installd:s0 tcontext=u:object_r:download_file:s0 tclass=file

Reproduction path is like below
1. Downloading Zipper application from Google Play (I used Zipper 1.9.9.2)
2. Clicking option and clicking "removing cache" button
3. Select "yes"
4. Violation show up

Change-Id: I7993f1d20e3aa4c3e19c4aba9b4bef6760831a87
Get rid of separate download_file type.

This appears to have been created to allow untrusted_app to
access DownloadProvider cache files without needing to allow
open access to platform_app_data_file.  Now that platform_app_data_file
is gone, there is no benefit to having this type.

Retain a typealias for download_file to app_data_file until
restorecon /data/data support is in place to provide compatibility.

This change depends on:
https://android-review.googlesource.com/#/c/87801/

Change-Id: Iab3c99d7d5448bdaa5c1e03a98fb6163804e1ec4
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
sepolicy: Fix more denials

 * Zygote needs to fork certan things
 * Installd needs to rename files

Change-Id: I643eace5af71dbd45a3c55518c516ea45bdefe07