make rapids-configure-conda-channels idempotent (#104)

tools/rapids-configure-conda-channels

@@ -1,11 +1,30 @@
 #!/bin/bash
 # A utility script that configures conda channels
 
+set -euo pipefail
+
+conda_channel_in_config() {
+  channel_id=${1:?err}
+  conda config --json --get channels \
+  | channel_id="${channel_id}" jq -r --exit-status '.get.channels | any(. == env.channel_id )'
+}
+
+# Only try to run 'conda config --remove' if the channel exists in the config.
+# This is here to avoid errors if this script is invoked multiple times in the same environment.
+remove_conda_channel() {
+  channel_id=${1:?err}
+  if conda_channel_in_config "${channel_id}" > /dev/null; then
+    conda config --system --remove channels "${channel_id}"
+  else
+    echo "[rapids-configure-conda-channels] channel '${channel_id}' not found via 'conda config --get channels'"
+  fi
+}
+
 # Remove nightly channels if build is a release build
 if rapids-is-release-build; then
-  conda config --system --remove channels rapidsai-nightly
-  conda config --system --remove channels dask/label/dev
+  remove_conda_channel 'rapidsai-nightly'
+  remove_conda_channel 'dask/label/dev'
 else
   # exclude stable channel from all non-release builds.
-  conda config --system --remove channels rapidsai
+  remove_conda_channel 'rapidsai'
 fi