PARQUET-83 : Hive Query failed if the data type is array<string>

Changed the  Parquet-Avro array definition to the Hive understandable.
Now with this fix Avro schema definition is going to be converted to the following format as below.
```
{ "name" : "action", "type" : [ { "type" : "array", "items" : "string" }, "null" ] }
```
Schema definition after this fix:
```
optional group action {
    repeated group bag {
        optional binary array_element
    }
}
```
This always sets the repetition of the array elements to optional, which means that they are always nullable. This should depend on whether the Avro schema for the array element is a union with null (optional) or not (required).

This also changes the name of the repeated field from "array" to "bag". I think this should be changed back because the field actually is an array, which implies that order matters, rather than a bag, which is closer to a `Collection`.