Make "weave attach" to depend on running weaver

"weave attach $CIDR $CONTAINER_ID" is no longer possible w/o
running weaver. This feature was undocumented and complicated
the weave script, as "weave attach" required to call "create_bridge".
Removing the feature allows us to eliminate the bridge creation
from the script.

Running "weave attach" w/o weaver results in the following err:

    bridge "weave" not present; did you launch weave?

Also, this commit simplifies the "attach-container" cmd from
weaveutil by removing "mtu" as a param. The cmd is used
only by "weave attach", and a mtu is value for an attached
container interface is exactly the same as one of the weave bridge.

prog/weaveutil/attach.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"net"
 	"os"
-	"strconv"
 	"strings"
 	"syscall"
 
@@ -15,8 +14,8 @@ import (
 )
 
 func attach(args []string) error {
-	if len(args) < 4 {
-		cmdUsage("attach-container", "[--no-multicast-route] [--keep-tx-on] [--hairpin-mode=true|false] <container-id> <bridge-name> <mtu> <cidr>...")
+	if len(args) < 3 {
+		cmdUsage("attach-container", "[--no-multicast-route] [--keep-tx-on] [--hairpin-mode=true|false] <container-id> <bridge-name> <cidr>...")
 	}
 
 	keepTXOn := false
@@ -52,16 +51,12 @@ func attach(args []string) error {
 	} else if nsHost.Equal(nsContainer) {
 		return fmt.Errorf("Container is running in the host network namespace, and therefore cannot be\nconnected to weave - perhaps the container was started with --net=host")
 	}
-	mtu, err := strconv.Atoi(args[2])
-	if err != nil && args[3] != "" {
-		return fmt.Errorf("unable to parse mtu %q: %s", args[2], err)
-	}
-	cidrs, err := parseCIDRs(args[3:])
+	cidrs, err := parseCIDRs(args[2:])
 	if err != nil {
 		return err
 	}
 
-	err = weavenet.AttachContainer(weavenet.NSPathByPid(pid), fmt.Sprint(pid), weavenet.VethName, args[1], mtu, withMulticastRoute, cidrs, keepTXOn, hairpinMode)
+	err = weavenet.AttachContainer(weavenet.NSPathByPid(pid), fmt.Sprint(pid), weavenet.VethName, args[1], 0, withMulticastRoute, cidrs, keepTXOn, hairpinMode)
 	// If we detected an error but the container has died, tell the user that instead.
 	if err != nil && !processExists(pid) {
 		err = fmt.Errorf("Container %s died", args[0])

weave

@@ -918,9 +918,7 @@ check_overlap() {
 }
 
 detect_awsvpc() {
-    # Ignoring errors here: if we cannot detect AWSVPC we will skip the relevant
-    # steps, because "attach" should work without the weave router running.
-    [ "$(call_weave GET /ipinfo/tracker)" != "awsvpc" ] || AWSVPC=1
+    [ "$(call_weave GET /ipinfo/tracker 2>/dev/null)" != "awsvpc" ] || AWSVPC=1
 }
 
 # Call IPAM as necessary to lookup or allocate addresses
@@ -1436,7 +1434,6 @@ case "$COMMAND" in
         done
         [ $# -eq 1 ] || usage
         CONTAINER=$(util_op container-id $1)
-        create_bridge
         ipam_cidrs allocate $CONTAINER $CIDR_ARGS
         if [ -n "$REWRITE_HOSTS" ] ; then
             # rewrite /etc/hosts, unlinking the file (so Docker does
@@ -1444,7 +1441,7 @@ case "$COMMAND" in
             util_op rewrite-etc-hosts "$CONTAINER" "$EXEC_IMAGE" "$ALL_CIDRS" $DNS_EXTRA_HOSTS
         fi
         [ -n "$AWSVPC" ] && ATTACH_ARGS="--no-multicast-route --keep-tx-on"
-        util_op attach-container $ATTACH_ARGS $CONTAINER $BRIDGE $MTU $ALL_CIDRS >/dev/null
+        util_op attach-container $ATTACH_ARGS $CONTAINER $BRIDGE $ALL_CIDRS >/dev/null
         [ -n "$WITHOUT_DNS" ] || when_weave_running with_container_fqdn $CONTAINER put_dns_fqdn $ALL_CIDRS
         show_addrs $ALL_CIDRS
         ;;