Add call to label to allow it to tell kernel how to label created files

SELinux supports a call that tells the kernel, from this point onward
create content with this label.  If you pass "", the kernel will
go back to the default.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Merge pull request #275 from rhatdan/selinux

Add call to label to allow it to tell kernel how to label created files