Add CLI tools for debugging and analyzing caching issues

[JiamingMai]

Add the following CLI tools for debugging and analyzing caching issues:

1. checkCaching. Checks if files under a path have been cached in alluxio.
2. location. Displays the list of hosts storing the specified file.
3. consistentHash. This command is for checking whether the consistent hash ring is changed or not.

[elega]

i think golang has strict lint rules... your code won't compile cc @Xenorith

[Xenorith]

the rule isn't enforced but you could run this command to recursively format the go files: https://golang.cafe/blog/how-to-run-gofmt-recursively.html

i will likely iterate on these new commands and add docs similar to what was done in #1814 so i am not too concerned about doing the cleanup now

[elega]

Please fix lint before merge

[Xenorith]

not blocking comments but if not addressed now, i will need to address them later

[JiamingMai]

alluxio-bot, merge this please