ZOOKEEPER-4468: Backport BCFKS key/trust store format support to branch 3.5

[symat]

Backporting ZOOKEEPER-3950 to branch-3.5.

This is a cherry-pick from #1482, also included checkstyle fix from #1516. This PR is basically the same as #1480 on the master branch, only the unit tests needed to be changed back from junit5 to junit4.

The BCFKS key store format is widely used in the industry, as it provides an open source alternative if someone has to use FIPS compliant key stores due to some regulatory constraints.

Currently in the ZooKeeper java client, only PEM, JKS and PEM12 is supported. I extend the list of supported key store formats with BCFKS.

I also tested this patch on a real FIPS compliant cluster, having the appropriate java security configs, security providers and also running a RedHat-based Linux distro (Centos 7.8) with FIPS mode enabled.

I tested both the client and the quorum SSL too. If someone wants to test this patch, and the keystore/truststore file names are not ending with ".bckfs", then (beside the usual SSL configs) make sure to also set the following parameters in the zoo.cfg:

ssl.keyStore.type=bcfks
ssl.trustStore.type=bcfks
ssl.quorum.keyStore.type=bcfks
ssl.quorum.trustStore.type=bcfks

and also provide the following parameters for the command line java client:

 -Dzookeeper.ssl.keyStore.type=bcfks -Dzookeeper.ssl.trustStore.type=bcfks

This patch doesn't contain any modification for the c-client (that can be handled with a separate Jira, but I don't plan to work on that part right now).

[fasiy]

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