SPEC-1221 DuplicateKey error is not reported as a top-level command error

[ShaneHarvey]

The old behavior was:

> session.startTransaction()
> session.getDatabase("test").runCommand({
   insert: 'c', 
   documents: [{_id: 0}, {_id: 0}]
})
{
    "ok" : 0,
    "errmsg" : "duplicate key error",
    "code" : 11000,
    "codeName" : "DuplicateKey"
}

The behavior after https://jira.mongodb.org/browse/SERVER-38583 is:

{
    "ok" : 1,
    "n" : 1,
    "writeErrors" : [
        {
            "index" : 1,
            "code" : 11000,
            "errmsg" : "duplicate key error"
        }
    ]
}

This error reporting change is going to be backported to 4.0.

For now I simply removed the errorCodeName: DuplicateKey assertions to get the tests to pass regardless of how the error is reported. Alternatively we could change the definition of errorCodeName to also look at error codes in writeErrors but since writeErrors don't have codeName we would either need to (re)introduce errorCode: 11000 or use the existing errorContains: duplicate key error.

[jyemin]

LGTM