In the case of running ostree as non-root on a regular filesystem (not
tmpfs which doesn't support immutable), we should just silently do
nothing if we encounter EPERM. Cache the result to avoid spam in
strace.
https://bugzilla.gnome.org/show_bug.cgi?id=728006
This prevents people from creating new directories there and expecting
them to be persisted. The OSTree model has all local state to be in
/etc and /var.
This introduces a compile-time dependency on libe2fsprogs.
We're only doing this for the root directory at the moment.
https://bugzilla.gnome.org/show_bug.cgi?id=728006