[ci] do not rely on PATH and installed mvn/ant - #6743

Failures:

  1) #4122 Stdio streams in a simple non-native JRuby instance should have sane fileno

     Failure/Error: expect(filenos[0]).to eq 0

     

     NoMethodError:

       undefined method `[]' for nil:NilClass

     # ./spec/regression/GH-4122_stdio_fileno_sanity_spec.rb:10:in `block in <main>'


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407 examples, 1 failure

Failed examples:

rspec ./spec/regression/GH-4122_stdio_fileno_sanity_spec.rb:8 # #4122 Stdio streams in a simple non-native JRuby instance should have sane fileno