Optimize circuit breaking state transformation using CAS in DegradeRule

[ATAXGT]

Describe what this PR does / why we need it

I feel that the method of modifying variables by synchronization is relatively poor, so I changed to CAS

Does this pull request fix one issue?

NONE

Describe how you did it

Modify the type of the property to AtomicBoolean and use compareAndSet method to change it.

Describe how to verify it

Use DegradeTest.java to verity it

Special notes for reviews

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #538 into master will decrease coverage by 0.09%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##             master     #538     +/-   ##
===========================================
- Coverage     38.24%   38.14%   -0.1%     
+ Complexity     1115     1111      -4     
===========================================
  Files           259      259             
  Lines          8174     8171      -3     
  Branches       1113     1113             
===========================================
- Hits           3126     3117      -9     
- Misses         4641     4644      +3     
- Partials        407      410      +3

Impacted Files	Coverage Δ	Complexity Δ
.../csp/sentinel/slots/block/degrade/DegradeRule.java	55.55% <66.66%> (-3.97%)	17 <7> (-1)
...ava/com/alibaba/csp/sentinel/node/ClusterNode.java	95.45% <0%> (-4.55%)	7% <0%> (-1%)
...a/csp/sentinel/slots/statistic/base/LeapArray.java	69.62% <0%> (-2.54%)	25% <0%> (-1%)
...l/cluster/server/connection/ConnectionManager.java	74% <0%> (-2%)	10% <0%> (-1%)

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[sczyh30]

LGTM

[sczyh30]

Thanks for contributing!