Add policy for run-as program.

Add policy for run-as program and label it in file_contexts.
Drop MLS constraints on local socket checks other than create/relabel
as this interferes with connections with services, in particular for
adb forward.

Change-Id: Ib0c4abeb7cbef559e150a620c45a7c31e0531114
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>