ARROW-5809: [CI] [Rust] Travis runs dockerized Rust build

[andygrove]

The specific nightly version of Rust is installed when building the Docker image, so it no longer needs to be downloaded on every run.

I have removed tarpaulin (code coverage) for now since it has been failing for many months anyway and there are challenges to getting it working with docker-compose. I will create a separate story for this.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-5809

[kou]

+1
We can merge this once CI is green.

I've pushed some small changes:

• `...` -> $(...)
• rust:1.38.0-stretch -> buster

[codecov-io]

Codecov Report

Merging #5586 into master will decrease coverage by 0.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5586      +/-   ##
==========================================
- Coverage   89.18%   88.82%   -0.37%     
==========================================
  Files         924      985      +61     
  Lines      127616   132477    +4861     
  Branches     1501     1501              
==========================================
+ Hits       113817   117670    +3853     
- Misses      13434    14442    +1008     
  Partials      365      365

Impacted Files	Coverage Δ
cpp/src/arrow/json/converter.cc	90.05% <0%> (-1.76%)	⬇️
cpp/src/arrow/json/chunked_builder.cc	80% <0%> (-1.67%)	⬇️
python/pyarrow/plasma.py	58.9% <0%> (-1.37%)	⬇️
cpp/src/arrow/compute/compute_test.cc	100% <0%> (ø)	⬆️
r/R/feather.R	63.33% <0%> (ø)
r/src/recordbatch.cpp	87.76% <0%> (ø)
r/src/table.cpp	87.61% <0%> (ø)
r/R/array-data.R	20% <0%> (ø)
r/R/filesystem.R	70.45% <0%> (ø)
r/R/list.R	100% <0%> (ø)
... and 62 more

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