refactor methods in presto-hive module

[pratyakshsharma]

There are many methods in presto-hive module which span few hundreds of lines and as a result, it is very difficult to go through them. Also these methods do not comply with the standard practices of coding. This PR is a small effort to refactor the code and break such long methods into smaller ones.

I believe this should be an ongoing effort to make the codebase more readable. Suggestions are welcome to point to other classes/methods which need refactoring as well.

Fill in the release notes towards the bottom of the PR description. See Release Notes Guidelines for details.

== RELEASE NOTES ==

General Changes
* Code refactoring - break long methods into small readable ones
* 

Hive Changes
* HiveSplitManager.java refactored
* StoragePartitionLoader.java refactored

If release note is NOT required, use:

== NO RELEASE NOTE ==

[pratyakshsharma]

@agrawalreetika @imjalpreet can you take the first pass here?

[pratyakshsharma]

@tdcmeehan I guess this is good to merge since it only involves some refactoring. Please have a look.

cc: @yzhang1991