Allow domain to read proc dirs.

Ability to read all of proc was placed in domain_deprecated with the
intention of reducing information leaking from proc.  Many processes try
to read proc dirs, though.  Allow this with the belief that information
leakage is from the proc files themselves rather than dir structure.

Address the following denial:
avc: denied { read } for name="/" dev="proc" ino=1 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:proc:s0 tclass=dir permissive=0

Bug: 26833472
Change-Id: I975ae022c093e1cf80de21487dc11e49f938e5a3