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ARROW-1331: [JAVA] Refactor unit tests

[cc @jacques-n , @StevenMPhillips ]

Refactored the java-vector unit tests in TestValueVector.java

(1) Moved all the BitVector related tests to TestBitVector.java
(2) Enhanced and added the tests for different vector types and grouped them into different categories in TestValueVector.java
(3) Moved https://github.com/dremio/dremio-oss/blob/master/sabot/kernel/src/test/java/com/dremio/exec/vector/TestSplitAndTransfer.java to arrow. This currently has splitAndTransfer() test for NullableVarCharVector.
(4) No tests have been removed -- they have either been enhanced or moved around for grouping.

Recently we added splitAndTransfer tests for BitVector, UnionVector and ListVector in their respective test files.  We should ideally move all the splitAndTransfer() related tests to TestSplitAndTransfer.java and should try to cover other vector types as well. A follow-up will address this (I want to keep the patch size small for easy review).

Author: siddharth <siddharth@dremio.com>

Closes #955 from siddharthteotia/ARROW-1331 and squashes the following commits:

ead5cef [siddharth] ARROW-1331: Fixed unit tests
2174e65 [siddharth] ARROW-1331: Refactor unit tests