LIVY-369. Add a full functionality SSL support for Livy server and client

[jerryshao]

Current LivyServer already supports SSL, but the functionality is not fully implemented, it cannot support client side authentication, also cannot specify advanced configurations. Also SSL support for Livy http client is missing.

So here propose to add a full functionality SSL support for Livy server and client.

[codecov-io]

Codecov Report

Merging #340 into master will decrease coverage by 1.74%.
The diff coverage is 14.97%.

@@             Coverage Diff              @@
##             master     #340      +/-   ##
============================================
- Coverage     70.46%   68.72%   -1.75%     
- Complexity      726      728       +2     
============================================
  Files            96       99       +3     
  Lines          5123     5295     +172     
  Branches        774      799      +25     
============================================
+ Hits           3610     3639      +29     
- Misses          996     1139     +143     
  Partials        517      517

Impacted Files	Coverage Δ	Complexity Δ
...ain/scala/com/cloudera/livy/server/WebServer.scala	65.3% <0%> (+3.76%)	10 <0> (ø)	⬇️
...om/cloudera/livy/client/http/ClientSSLOptions.java	0% <0%> (ø)	0 <0> (?)
...la/com/cloudera/livy/server/ServerSSLOptions.scala	0% <0%> (ø)	0 <0> (?)
...va/com/cloudera/livy/client/common/SSLOptions.java	0% <0%> (ø)	0 <0> (?)
...n/java/com/cloudera/livy/client/http/HttpConf.java	81.66% <100%> (+3.66%)	5 <0> (ø)	⬇️
...er/src/main/scala/com/cloudera/livy/LivyConf.scala	94.81% <100%> (+0.45%)	16 <0> (ø)	⬇️
.../com/cloudera/livy/client/http/LivyConnection.java	77.46% <40%> (-3.14%)	15 <3> (ø)
...n/scala/com/cloudera/livy/utils/SparkYarnApp.scala	61.26% <0%> (-0.44%)	29% <0%> (ø)
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2abb8a3...2546868. Read the comment docs.