More descriptive / detailed error expected

[DenisBalan]

When running on a fresh ubuntu vm
containerd-rootless-setuptool.sh check or rootlesskit bash

Got strange error

ubuntu@energetic-anemone:~$ containerd-rootless-setuptool.sh check
[INFO] Checking RootlessKit functionality
[rootlesskit:parent] error: failed to start the child: fork/exec /proc/self/exe: operation not permitted
[ERROR] RootlessKit failed, see the error messages and https://rootlesscontaine.rs/getting-started/common/ .

https://github.com/containerd/nerdctl/blob/35f22c7bf0cd011077c1cb0429a58730fb5be411/extras/rootless/containerd-rootless-setuptool.sh#L110

Turn out containerd-rootless-setuptool.sh is not well description enough to provide resolution (as rootlesskit bash is doing)
Or at least to pipe whole output from inner rootlesskit process

	INFO "Checking RootlessKit functionality"
	if ! rootlesskit \
		--net=slirp4netns \
		--disable-host-loopback \
		--copy-up=/etc --copy-up=/run --copy-up=/var/lib \
		true; then
		ERROR "RootlessKit failed, see the error messages and https://rootlesscontaine.rs/getting-started/common/ ."
		exit 1
	fi

It took some time until I figured out that there is similar issue, see also #425