ARROW-7341: [CI] Unbreak nightly Conda R job

[nealrichardson]

One fix, one minor improvement, and also alphabetizing the env vars.

[nealrichardson]

@ursabot crossbow submit conda-r

[ursabot]

AMD64 Conda Crossbow Submit (#81568) builder failed.

Revision: a45fe3b

Crossbow: 'python crossbow.py ...' step's stderr:

Error: Invalid task(s) {'conda-r'}. Must be one of {'centos-8-aarch64', 'wheel-win-cp36m', 'wheel-osx-cp37m', 'ubuntu-eoan', 'debian-buster-arm64', 'conda-linux-gcc-py36', 'conda-osx-clang-py37', 'macos-r-autobrew', 'wheel-manylinux1-cp37m', 'test-conda-python-3.7-dask-latest', 'gandiva-jar-osx', 'ubuntu-bionic', 'test-ubuntu-18.04-r-sanitizer', 'test-ubuntu-18.04-cpp', 'debian-stretch', 'test-conda-r-3.6', 'ubuntu-eoan-arm64', 'wheel-win-cp37m', 'test-conda-python-2.7-pandas-latest', 'test-conda-python-3.7-turbodbc-master', 'wheel-osx-cp35m', 'ubuntu-xenial-arm64', 'test-conda-python-3.8-pandas-latest', 'wheel-manylinux2010-cp27m', 'ubuntu-bionic-arm64', 'debian-stretch-arm64', 'test-conda-python-2.7', 'test-ubuntu-18.04-cpp-cmake32', 'test-ubuntu-18.04-python-3', 'test-conda-python-3.7-spark-master', 'test-ubuntu-16.04-cpp', 'test-conda-python-3.7-pandas-latest', 'conda-linux-gcc-py37', 'wheel-manylinux1-cp27m', 'test-conda-python-3.8-dask-master', 'homebrew-cpp-autobrew', 'wheel-manylinux2010-cp35m', 'centos-8', 'test-fedora-29-cpp', 'centos-7', 'wheel-manylinux2010-cp37m', 'conda-osx-clang-py27', 'test-conda-python-3.7-hdfs-2.9.2', 'test-conda-python-3.7-turbodbc-latest', 'test-debian-10-go-1.12', 'test-ubuntu-fuzzit-regression', 'test-debian-10-cpp', 'test-debian-ruby', 'test-ubuntu-ruby', 'test-conda-python-3.6', 'test-ubuntu-18.04-cpp-release', 'wheel-manylinux2010-cp36m', 'wheel-osx-cp27m', 'gandiva-jar-trusty', 'conda-win-vs2015-py37', 'centos-6', 'test-ubuntu-c-glib', 'test-debian-c-glib', 'test-conda-python-3.7-pandas-master', 'test-conda-cpp', 'wheel-manylinux1-cp35m', 'wheel-manylinux1-cp27mu', 'homebrew-cpp', 'conda-linux-gcc-py27', 'wheel-manylinux1-cp36m', 'test-ubuntu-fuzzit-fuzzing', 'wheel-osx-cp36m', 'conda-win-vs2015-py36', 'test-conda-python-3.7', 'test-conda-python-3.8', 'wheel-osx-cp37m-azure', 'test-ubuntu-18.04-r-3.6', 'wheel-manylinux2010-cp27mu', 'debian-buster', 'ubuntu-disco', 'test-conda-cpp-hiveserver2', 'ubuntu-xenial', 'centos-7-aarch64', 'conda-osx-clang-py36', 'test-ubuntu-18.04-cpp-static', 'test-fedora-29-python-3', 'ubuntu-disco-arm64', 'test-debian-10-python-3', 'test-ubuntu-18.04-docs'}

[nealrichardson]

@ursabot crossbow submit test-conda-r-3.6

[ursabot]

AMD64 Conda Crossbow Submit (#81569) builder has been succeeded.

Revision: a45fe3b

Submitted crossbow builds: ursa-labs/crossbow @ ursabot-381

Task	Status
test-conda-r-3.6

[nealrichardson]

I canceled the appveyor job to unclog the queue; this patch does not affect appveyor.

[nealrichardson]

@ursabot crossbow submit test-conda-r-3.6

[ursabot]

AMD64 Conda Crossbow Submit (#81571) builder has been succeeded.

Revision: 61c36b1

Submitted crossbow builds: ursa-labs/crossbow @ ursabot-383

Task	Status
test-conda-r-3.6

[nealrichardson]

Crossbow job passed: https://circleci.com/gh/ursa-labs/crossbow/5776