LIVY-358. Make JettyServer Http request and response header size configurable

[jerryshao]

This patch is based on #266 , mainly to fix header size too large problem in spnego enabled scenario.

1. Increase the default header size.
2. Make header size configurable.

[codecov-io]

Codecov Report

Merging #329 into master will decrease coverage by 0.06%.
The diff coverage is 84.61%.

@@             Coverage Diff              @@
##             master     #329      +/-   ##
============================================
- Coverage     70.55%   70.48%   -0.07%     
+ Complexity      726      724       -2     
============================================
  Files            96       96              
  Lines          5121     5123       +2     
  Branches        774      774              
============================================
- Hits           3613     3611       -2     
- Misses          990      995       +5     
+ Partials        518      517       -1

Impacted Files	Coverage Δ	Complexity Δ
...er/src/main/scala/com/cloudera/livy/LivyConf.scala	94.35% <100%> (-0.09%)	16 <0> (ø)
...ain/scala/com/cloudera/livy/server/WebServer.scala	59.61% <66.66%> (-0.81%)	9 <0> (ø)
rsc/src/main/java/com/cloudera/livy/rsc/Utils.java	83.33% <0%> (-2.39%)	16% <0%> (ø)
...n/java/com/cloudera/livy/rsc/driver/RSCDriver.java	76.29% <0%> (-2.16%)	39% <0%> (-1%)
...c/src/main/java/com/cloudera/livy/rsc/rpc/Rpc.java	77.98% <0%> (-0.63%)	12% <0%> (ø)
.../java/com/cloudera/livy/rsc/driver/JobWrapper.java	80.64% <0%> (ø)	7% <0%> (-1%)	⬇️
...in/java/com/cloudera/livy/rsc/ContextLauncher.java	83.08% <0%> (+2.48%)	19% <0%> (ø)	⬇️

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[zjffdu]

LGTM