ARROW-4566: [Flight] Add option to run Flight benchmark against separate server

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[codecov-io]

Codecov Report

Merging #4103 into master will increase coverage by 0.79%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4103      +/-   ##
==========================================
+ Coverage   87.83%   88.62%   +0.79%     
==========================================
  Files         739      604     -135     
  Lines       90965    81301    -9664     
  Branches     1252        0    -1252     
==========================================
- Hits        79896    72057    -7839     
+ Misses      10948     9244    -1704     
+ Partials      121        0     -121

Impacted Files	Coverage Δ
cpp/src/arrow/csv/column-builder.cc	95.32% <0%> (-1.76%)	⬇️
cpp/src/arrow/util/thread-pool-test.cc	97.66% <0%> (-0.94%)	⬇️
go/arrow/math/uint64_amd64.go
go/arrow/memory/memory_avx2_amd64.go
js/src/enum.ts
go/arrow/array/builder.go
js/src/Arrow.node.ts
js/src/schema.ts
go/arrow/type_traits_boolean.go
js/src/ipc/node/writer.ts
... and 127 more

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[wesm]

+1, thank you!