change renew expired duration to 15s

[dzdx]

requirements:
renew expired duration < sessionOff duration

[codecov-io]

Codecov Report

Merging #145 into master will decrease coverage by 0.20%.
The diff coverage is 42.72%.

@@             Coverage Diff              @@
##             master     #145      +/-   ##
============================================
- Coverage     62.25%   62.04%   -0.21%     
  Complexity       44       44              
============================================
  Files           429      437       +8     
  Lines         15505    15802     +297     
  Branches       1490     1502      +12     
============================================
+ Hits           9652     9804     +152     
- Misses         4840     4983     +143     
- Partials       1013     1015       +2     

Impacted Files	Coverage Δ	Complexity Δ
.../model/metaserver/ConfigureLoadbalanceRequest.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...model/metaserver/GetLoadbalanceMetricsRequest.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...ry/common/model/metaserver/LoadbalanceMetrics.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...gistry/server/meta/bootstrap/MetaServerConfig.java	100.00% <ø> (ø)	0.00 <0.00> (ø)
.../server/meta/node/impl/SessionNodeServiceImpl.java	33.07% <0.00%> (-23.69%)	0.00 <0.00> (ø)
...istry/server/meta/registry/MetaServerRegistry.java	61.11% <0.00%> (-5.56%)	0.00 <0.00> (ø)
...eta/remoting/connection/DataConnectionHandler.java	66.66% <ø> (ø)	0.00 <0.00> (ø)
...eta/remoting/connection/MetaConnectionHandler.java	15.00% <ø> (ø)	0.00 <0.00> (ø)
.../remoting/connection/SessionConnectionHandler.java	70.58% <ø> (ø)	0.00 <0.00> (ø)
.../server/meta/remoting/handler/DataNodeHandler.java	72.72% <ø> (ø)	0.00 <0.00> (ø)
... and 46 more

---

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[nocvalight]

LGTM

[quhongwei]

LGTM