Use a more informative API response when updating a user

[pantelis-karamolegkos]

I think one cannot tell from the API response whether the user was actually updated or not.

POST /_security/user/jacknich
{
  "password" : "l0ng-r4nd0m-p@ssw0rd",
  "roles" : [ "admin" ],
  "full_name" : "Jack Nicholson",
  "email" : "jacknich@example.com",
  "metadata" : {
    "intelligence" : 7
  }
}

{
  "created" : true
}

PUT /_security/user/jacknich
{
  "password" : "l0ng-r4nd0m-p@ssw0rd",
  "roles" : [ "colonel" ],
  "full_name" : "Nathan Jessup",
  "email" : "jacknich@example.com",
  "metadata" : {
    "intelligence" : 7
  }
}

{
  "created" : false
}

...and again

PUT /_security/user/jacknich
{
  "password" : "l0ng-r4nd0m-p@ssw0rd",
  "roles" : [ "colonel" ],
  "full_name" : "Nathan Jessup",
  "email" : "jacknich@example.com",
  "metadata" : {
    "intelligence" : 7
  }
}

{
  "created" : false
}

[elasticmachine]

Pinging @elastic/es-security (Team:Security)