Handle DOCKER_HOST environment for podman-docker package

Rootless users should be defaulted to point DOCKER_HOST at
$XDG_RUNTIME_DIR/podman/podman.sock

When podman-docker package is installed.

[NO NEW TESTS NEEDED]

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

docker/docker.in

@@ -0,0 +1,4 @@
+#!/bin/sh
+[ -e ${ETCDIR}/containers/nodocker ] || \
+echo "Emulate Docker CLI using podman. Create ${ETCDIR}/containers/nodocker to quiet msg." >&2
+exec ${BINDIR}/podman "$@"

docker/podman-docker.csh

@@ -0,0 +1,10 @@
+# DOCKER_HOST initialization
+
+if ($?DOCKER_HOST) exit
+if ( "$euid" == 0 ) then
+        setenv DOCKER_HOST unix:///run/podman/podman.sock
+else
+    if ($?XDG_RUNTIME_DIR) then
+        setenv DOCKER_HOST unix://$XDG_RUNTIME_DIR/podman/podman.sock
+    endif
+endif

docker/podman-docker.sh

@@ -0,0 +1,11 @@
+# DOCKER_HOST initialization
+
+if [ -z "$DOCKER_HOST" ]; then
+    if [ $(id -u) -eq 0 ]; then
+	export DOCKER_HOST=unix:///run/podman/podman.sock
+    else
+	if [ -n "$XDG_RUNTIME_DIR" ]; then
+	    export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/podman/podman.sock
+	fi
+    fi
+fi