[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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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 #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