Add charset and collation to google_sql_database. (hashicorp#183)

* Add charset and collation to google_sql_database.

* Add documentation for charset, collation attributes.

* Extend the existing acceptance test to also cover charset and collation.

* Charset and collation always have a value present. Also inline.

* Move charset and collation to optional arguments.

* Add charset and collection to the example.

* Document charset and collation defaults.

* Keep TestAccGoogleSqlDatabase_basic as is, add TestAccGoogleSqlDatabase_update.

docs/r/sql_database.html.markdown

@@ -24,8 +24,10 @@ resource "google_sql_database_instance" "master" {
 }
 
 resource "google_sql_database" "users" {
-  name     = "users-db"
-  instance = "${google_sql_database_instance.master.name}"
+  name      = "users-db"
+  instance  = "${google_sql_database_instance.master.name}"
+  charset   = "latin1"
+  collation = "latin1_swedish_ci"
 }
 ```
 
@@ -42,6 +44,11 @@ The following arguments are supported:
 * `project` - (Optional) The project in which the resource belongs. If it
     is not provided, the provider project is used.
 
+* `charset` - (Optional) The MySQL charset value (default "utf8").
+
+* `collation` - (Optional) The MySQL collation value (default
+    "utf8_general_ci").
+
 ## Attributes Reference
 
 In addition to the arguments listed above, the following computed attributes are