scope launch script: Fix and consolidate usage info

Instead of different usage info for "scope help", show the same always.
Also correct it for what the script actually does,
and always display the scope binary args.

scope

@@ -3,17 +3,6 @@
 set -eu
 
 ARGS="$*"
-
-usage() {
-    echo "Usage:"
-    echo "scope launch [<peer> ...]"
-    echo "scope stop"
-    echo "scope command"
-    echo
-    echo "scope <peer>    is of the form <ip_address_or_fqdn>[:<port>]"
-    exit 1
-}
-
 SCRIPT_VERSION="(unreleased version)"
 if [ "$SCRIPT_VERSION" = "(unreleased version)" ] ; then
     IMAGE_VERSION=latest
@@ -30,7 +19,29 @@ IP_ADDR_CMD="find /sys/class/net -type l | xargs -n1 basename | grep -vE 'docker
     xargs -n1 ip addr show | grep inet | awk '{ print \$2 }' | grep -oE '$IP_REGEXP'"
 WEAVESCOPE_DOCKER_ARGS=${WEAVESCOPE_DOCKER_ARGS:-}
 
-[ $# -gt 0 ] || usage
+usage() {
+    name=$(basename "$0")
+    cat >&2 <<-EOF
+		Usage:
+		$name launch {ARGS} - Launch Scope
+		$name stop          - Stop Scope
+		$name command       - Print the docker command used to start Scope
+		$name help          - Print usage info
+		$name version       - Print version info
+
+		Launch arguments:
+	EOF
+    docker run --rm -e CHECKPOINT_DISABLE --entrypoint=/home/weave/scope \
+        $WEAVESCOPE_DOCKER_ARGS "$SCOPE_IMAGE" -h >&2 ||
+        echo "Error listing launch arguments" >&2
+}
+
+usage_and_die() {
+    usage
+    exit 1
+}
+
+[ $# -gt 0 ] || usage_and_die
 COMMAND=$1
 shift 1
 
@@ -190,23 +201,7 @@ case "$COMMAND" in
         ;;
 
     help)
-        cat >&2 <<EOF
-Usage:
-
-scope help     - Print this
-
-scope launch   - Launch Scope
-EOF
-        docker run --rm -e CHECKPOINT_DISABLE --entrypoint=/home/weave/scope \
-            $WEAVESCOPE_DOCKER_ARGS "$SCOPE_IMAGE" -h
-
-        cat >&2 <<EOF
-
-scope stop     - Stop Scope
-
-scope command  - Print the docker command used to start Scope
-
-EOF
+        usage
         ;;
 
     launch)
@@ -247,7 +242,7 @@ EOF
         ;;
 
     stop)
-        [ $# -eq 0 ] || usage
+        [ $# -eq 0 ] || usage_and_die
         if docker inspect "$SCOPE_CONTAINER_NAME" >/dev/null 2>&1 ; then
            docker stop "$SCOPE_CONTAINER_NAME" >/dev/null
         fi
@@ -260,7 +255,7 @@ EOF
 
     *)
         echo "Unknown scope command '$COMMAND'" >&2
-        usage
+        usage_and_die
         ;;
 
 esac