Added support for authMechanismProperties on the connection string

JAVA-1466
The logic is the same as `parseOptions` - I'll remove the final keyword there also.

No comma at all is handled as it will just have a single part.  
No colon in each property is also handled as they are ignored in the same way as options are.

I did have add a test for invalid separator and I've moved it out into its own block.