Extend forkAndSpecialize to take additional inputs and to set the SELinux security context.

forkAndSpecialize presently sets the DAC credentials for the app process.
Modify it to invoke libselinux to set the SELinux security context as well.
Extend it to take additional inputs from the caller in order to provide
more selectors for deciding what SELinux security context to use.

Change-Id: I2611671ad6f10ce3d8cbda8471bcacb8c9955546
2 files changed