refactor: make proxy log via a package-local var

which gets rid of a bunch of (dot) imports.

proxy/create_exec_interceptor.go

@@ -3,8 +3,6 @@ package proxy
 import (
 	"net/http"
 	"strings"
-
-	. "github.com/weaveworks/weave/common"
 )
 
 type createExecInterceptor struct{ proxy *Proxy }