[BC] CreateMode: refactor and fix FlagX Create flags.

[jeffbean]

BREAKING Client behavior: since this proposes a new parsing of the Create flag integer this will break clients if they rely on CreateContainer as it was creating znodes that may not have been containers.

Changes:

• Fix FlagTTL value from 4 -> 5
• Adding all known CreateMode values to Flag constants.
• Adding a createMode private struct behind the flag integer, replicate CreateMode from ZK java lib.
• Create, CreateContainer, CreateTTL methods now parse the flag integer passed in based on the constants defined (new error condition).
• Rewrite tests to better catch CreateContainer and CreateTTL (no assertions on zk behavior since zk does not expose znode mode)
• Added Change-Detector unit tests for create mode values.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.50%. Comparing base (6131812) to head (b61590a).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #136 +/- ## ========================================== + Coverage 77.98% 78.50% +0.51% ========================================== Files 7 8 +1 Lines 1322 1349 +27 ========================================== + Hits 1031 1059 +28 Misses 199 199 + Partials 92 91 -1 ```

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[jeffbean]

Based on the PR https://github.com/go-zookeeper/zk/pull/125 that shows the issue at hand. The bug was in the CreateContainer and CreateTTL methods.

[jeffbean]

For others that may face new errors:

    path, err := c.CreateContainer("/container-node", []byte("foo"), zk.FlagTTL, zk.WorldACL(zk.PermAll))
    if err != nil {
        log.Fatal(err)
    }
// old: would not error, and create a Container znode
// new: will return an error that this is not a TTL operation and not create a znode