Issue 6620: Make fetching tokens on segment reader creation async

[tkaitchuck]

Signed-off-by: Tom Kaitchuck tom.kaitchuck@emc.com

Change log description
Make fetching tokens on segment reader creation async

Purpose of the change
Fixes #6620

What the code does
Makes the token fetching upon creation of a new segment reader asynchronous.

[codecov]

Codecov Report

Merging #6622 (b8f5bd8) into master (136e14e) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #6622      +/-   ##
============================================
+ Coverage     86.28%   86.31%   +0.03%     
- Complexity    15646    15656      +10     
============================================
  Files          1017     1017              
  Lines         58696    58694       -2     
  Branches       5948     5948              
============================================
+ Hits          50644    50663      +19     
+ Misses         4942     4928      -14     
+ Partials       3110     3103       -7     

Impacted Files	Coverage Δ
...a/client/byteStream/impl/ByteStreamClientImpl.java	100.00% <100.00%> (ø)
...nt/segment/impl/SegmentInputStreamFactoryImpl.java	87.50% <100.00%> (-0.74%)	⬇️
...a/segmentstore/server/logs/OperationProcessor.java	88.88% <0.00%> (-1.80%)	⬇️
...tore/server/containers/StreamSegmentContainer.java	89.64% <0.00%> (-0.67%)	⬇️
...main/java/io/pravega/storage/hdfs/HDFSStorage.java	73.33% <0.00%> (+0.31%)	⬆️
.../segmentstore/server/writer/SegmentAggregator.java	80.17% <0.00%> (+0.42%)	⬆️
...ver/containers/StreamSegmentContainerMetadata.java	97.45% <0.00%> (+0.63%)	⬆️
...client/control/impl/ControllerResolverFactory.java	83.80% <0.00%> (+0.95%)	⬆️
.../server/attributes/SegmentAttributeBTreeIndex.java	90.98% <0.00%> (+1.09%)	⬆️
...ga/controller/store/client/StoreClientFactory.java	81.03% <0.00%> (+1.72%)	⬆️
... and 3 more

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[ShwethaSNayak]

LGTM. Async way of fetching delegation token while creating segment reader will definitely improve the performance.

[sachin-j-joshi]

LGTM