[BEAM-6083] share parsing functions to parse time among SQL tests

[amaliujia]

Sharing time parsing functions among SQL tests.

The benefits are:

1. new Datetime() way looks too long in IDE and makes code hard to read.
2. In tests, if data is written into query (e.g. "SELECT DATE '2018-01-30'"), then that string can be copied to parsing functions for query result match (compared to write a new Datetime.
3. Reduce confusion of with/without timezone when creating a new Joda Datetime.
4. Well formatted datetime string is more readable.

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---	---	---	---	---
Java
Python		---			---	---	---

[amaliujia]

@apilloud @akedin @kennknowles

[amaliujia]

run java postcommit

[amaliujia]

run java postcommit