Add keystore to AID_READPROC

keystore access /proc entries associated with other UIDs.
Allow it.

Bug: 23310674
Change-Id: I72fa3fa3df5d7c8c359b5a78fe89d7f7cdb8ab24

keystore/keystore.rc

 service keystore /system/bin/keystore /data/misc/keystore
     class main
     user keystore
-    group keystore drmrpc
+    group keystore drmrpc readproc