proxy needs to add weavewait to execs as well

Bug came up in a test where we are restarting and doing an exec checking
a network interface right away. weavewait is only added if the container
has a WEAVE_CIDR var set, the same as at container creation.

proxy/common.go

@@ -1,13 +1,24 @@
 package proxy
 
 import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
 	"os/exec"
+	"regexp"
 	"strings"
 
 	"github.com/fsouza/go-dockerclient"
 	. "github.com/weaveworks/weave/common"
 )
 
+var (
+	containerIDRegexp   = regexp.MustCompile("^/v[0-9\\.]*/containers/([^/]*)/.*")
+	weaveWaitEntrypoint = []string{"/home/weavewait/weavewait"}
+)
+
 func callWeave(args ...string) ([]byte, error) {
 	args = append([]string{"--local"}, args...)
 	Debug.Print("Calling weave", args)
@@ -26,3 +37,29 @@ func weaveCIDRsFromConfig(config *docker.Config) ([]string, bool) {
 	}
 	return nil, false
 }
+
+func marshalRequestBody(r *http.Request, body interface{}) error {
+	newBody, err := json.Marshal(body)
+	if err != nil {
+		return err
+	}
+	r.Body = ioutil.NopCloser(bytes.NewReader(newBody))
+	r.ContentLength = int64(len(newBody))
+	return nil
+}
+
+func inspectContainerInPath(client *docker.Client, path string) (*docker.Container, error) {
+	subs := containerIDRegexp.FindStringSubmatch(path)
+	if subs == nil {
+		err := fmt.Errorf("No container id found in request with path %s", path)
+		Warning.Println(err)
+		return nil, err
+	}
+	containerID := subs[1]
+
+	container, err := client.InspectContainer(containerID)
+	if err != nil {
+		Warning.Printf("Error inspecting container %s: %v", containerID, err)
+	}
+	return container, err
+}