[FLINK-9684][historyserver] HistoryServer should initialize FileSystem before using it

[Ethanlm]

What is the purpose of the change

Details explained in https://issues.apache.org/jira/browse/FLINK-9684 . This pull request makes HistoryServer initialize FileSystem before using it. That way HistoryServerArchiveFetcher will be able to talk to secure hdfs correctly.

Brief change log

• HistoryServer initializes FileSystem before using it

Verifying this change

This change added tests and can be verified as follows:

• Manually verified the change by running a historyserver with kerberos-secured hdfs cluster.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

[Ethanlm]

Just realized fs.hdfs.hadoopconf is deprecated and we want to use HADOOP_CONF_DIR instead.
https://github.com/apache/flink/blob/master/flink-core/src/main/java/org/apache/flink/configuration/ConfigConstants.java#L652-L658

Not sure why we are doing it. But if HADOOP_CONF_DIR is set explicitly, HistoryServer should work fine.

However, I believe we still need to initialize FileSystem before using it.

[tillrohrmann]

Thanks for opening the PR @Ethanlm. Changes look good to me. Merging this PR.