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)
I believe this could fail if SELinux is disabled.  Since it is trying to write to /proc/self/attr/create, if this file does not exist because SELinux is disabled the call will fail and bubble up an error.