mongo stuff to agent/mongod, add EnsureMongoServer

provider/local/prereqs.go

 // Copyright 2013 Canonical Ltd.
 // Licensed under the AGPLv3, see LICENCE file for details.
 
 package local
 
 import (
         "errors"
         "fmt"
         "os/exec"
         "regexp"
@@ skipping 65 matching lines @@
         switch containerType {
         case instance.LXC:
                 return verifyLxc()
         case instance.KVM:
                 return kvm.VerifyKVMEnabled()
         }
         return fmt.Errorf("Unknown container type specified in the config.")
 }
 
 func verifyMongod() error {
-        path := mongo.MongodPath()
+        path, err := mongo.MongodPath()
+        if err != nil {
+                return err
+        }
 
         ver, err := mongodVersion(path)
         if err != nil {
                 return err
         }
         if ver.Compare(lowestMongoVersion) < 0 {
                 return fmt.Errorf("installed version of mongod (%v) is not supported by Juju. "+
                         "Juju requires version %v or greater.",
                         ver,
                         lowestMongoVersion)
@@ skipping 40 matching lines @@
         }
         return fmt.Errorf("%v\n%s", err, installMongodGeneric)
 }
 
 func wrapLxcNotFound(err error) error {
         if utils.IsUbuntu() {
                 return fmt.Errorf("%v\n%s", err, installLxcUbuntu)
         }
         return fmt.Errorf("%v\n%s", err, installLxcGeneric)
 }