run-as: Get seinfo from packages.list and pass to libselinux.

Change allows the proper seinfo value to be passed
to libselinux to switch to the proper app security
context before running the shell.

Change-Id: I9d7ea47c920b1bc09a19008345ed7fd0aa426e87
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>