Add ability to run k3s as non-root user

[erikwilson]

When attempting to run release binary k3s server as non-root we prepare a data directory:

INFO[0000] Preparing data dir /home/test/.rancher/k3s/data/XXX
FATA[2019-02-25T17:19:39.192549600Z] must run as root unless --disable-agent is specified

but further attempts to run as non-root result in an error:

FATA[0000] exec: "k3s-server": executable file not found in $PATH

[ibuildthecloud]

Related or the same issue #21

[dnoland1]

Works with v0.2.0-rc6:

ubuntu@k3s-node1:~$ id
uid=1000(ubuntu) gid=1000(ubuntu) groups=1000(ubuntu),4(adm),20(dialout),24(cdrom),25(floppy),27(sudo),29(audio),30(dip),44(video),46(plugdev),110(netdev),111(lxd)
ubuntu@k3s-node1:~$ ./k3s server --disable-agent
INFO[2019-03-08T04:32:34.679276979Z] Starting k3s v0.2.0-rc6 (2771ae1)
INFO[2019-03-08T04:32:35.896017650Z] Running kube-apiserver --watch-cache=false --cert-dir /home/ubuntu/.rancher/k3s/server/tls/temporary-certs --allow-privileged=true --authorization-mode Node,RBAC --service-account-signing-key-file /home/ubuntu/.rancher/k3s/server/tls/service.key --service-cluster-ip-range 10.43.0.0/16 --advertise-port 6445 --advertise-address 127.0.0.1 --insecure-port 0 --secure-port 6444 --bind-address 127.0.0.1 --tls-cert-file /home/ubuntu/.rancher/k3s/server/tls/localhost.crt --tls-private-key-file /home/ubuntu/.rancher/k3s/server/tls/localhost.key --service-account-key-file /home/ubuntu/.rancher/k3s/server/tls/service.key --service-account-issuer k3s --api-audiences unknown --basic-auth-file /home/ubuntu/.rancher/k3s/server/cred/passwd --kubelet-client-certificate /home/ubuntu/.rancher/k3s/server/tls/token-node.crt --kubelet-client-key /home/ubuntu/.rancher/k3s/server/tls/token-node.key
INFO[2019-03-08T04:32:37.209801481Z] Running kube-scheduler --kubeconfig /home/ubuntu/.rancher/k3s/server/cred/kubeconfig-system.yaml --port 10251 --address 127.0.0.1 --secure-port 0 --leader-elect=false
INFO[2019-03-08T04:32:37.211504506Z] Running kube-controller-manager --kubeconfig /home/ubuntu/.rancher/k3s/server/cred/kubeconfig-system.yaml --service-account-private-key-file /home/ubuntu/.rancher/k3s/server/tls/service.key --allocate-node-cidrs --cluster-cidr 10.42.0.0/16 --root-ca-file /home/ubuntu/.rancher/k3s/server/tls/token-ca.crt --port 10252 --address 127.0.0.1 --secure-port 0 --leader-elect=false
Flag --address has been deprecated, see --bind-address instead.
INFO[2019-03-08T04:32:37.389503594Z] Creating CRD listenerconfigs.k3s.cattle.io
INFO[2019-03-08T04:32:37.416034969Z] Creating CRD addons.k3s.cattle.io
INFO[2019-03-08T04:32:37.427321802Z] Creating CRD helmcharts.k3s.cattle.io
INFO[2019-03-08T04:32:37.459529124Z] Waiting for CRD listenerconfigs.k3s.cattle.io to become available
INFO[2019-03-08T04:32:37.961566620Z] Done waiting for CRD listenerconfigs.k3s.cattle.io to become available
INFO[2019-03-08T04:32:37.962033975Z] Waiting for CRD addons.k3s.cattle.io to become available
INFO[2019-03-08T04:32:38.465847971Z] Done waiting for CRD addons.k3s.cattle.io to become available
INFO[2019-03-08T04:32:38.466789685Z] Waiting for CRD helmcharts.k3s.cattle.io to become available
INFO[2019-03-08T04:32:38.970526981Z] Done waiting for CRD helmcharts.k3s.cattle.io to become available
INFO[2019-03-08T04:32:38.972947943Z] Listening on :6443
INFO[2019-03-08T04:32:39.761363086Z] Node token is available at /home/ubuntu/.rancher/k3s/server/node-token
INFO[2019-03-08T04:32:39.766048704Z] To join node to cluster: k3s agent -s https://10.0.2.15:6443 -t ${NODE_TOKEN}
INFO[2019-03-08T04:32:39.765798683Z] Writing manifest: /home/ubuntu/.rancher/k3s/server/manifests/coredns.yaml
INFO[2019-03-08T04:32:39.770124190Z] Writing manifest: /home/ubuntu/.rancher/k3s/server/manifests/traefik.yaml
INFO[2019-03-08T04:32:40.068422826Z] Wrote kubeconfig /home/ubuntu/.kube/k3s.yaml
INFO[2019-03-08T04:32:40.069537204Z] Run: k3s kubectl
INFO[2019-03-08T04:32:40.069837608Z] k3s is up and running