label: tweak LabelOps post() hook to take "created" boolean

label: tweak LabelOps post() hook to take "created" boolean

We have two distinct implementations of the post hook.

1. For SELinux we just reset the selinux label we told the kernel
   earlier to use for new inodes.

2. For SMACK we might apply an xattr to the specified file.

The two calls are quite different: the first call we want to call in all
cases (failure or success), the latter only if we actually managed to
create an inode, in which case it is called on the inode.