Refactor not leader logic

[birdstorm]

resolves #411

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@21fe913). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master     #412   +/-   ##
=========================================
  Coverage          ?   55.08%           
=========================================
  Files             ?      127           
  Lines             ?     5844           
  Branches          ?      879           
=========================================
  Hits              ?     3219           
  Misses            ?     2327           
  Partials          ?      298

Impacted Files	Coverage Δ
...in/java/com/pingcap/tikv/region/RegionManager.java	60.57% <0%> (ø)
...ava/com/pingcap/tikv/region/RegionStoreClient.java	57.39% <0%> (ø)
...ava/com/pingcap/tikv/operation/KVErrorHandler.java	23.15% <0%> (ø)

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[birdstorm]

@ilovesoup PTAL

[birdstorm]

/run-all-tests

[ilovesoup]

LGTM