Factor out common environment setup GHA steps

Tools/CI-linux-environment.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+# Expected to be called from elsewhere with same variables set as CI-linux-install.sh
+# e.g. RETRY=travis-retry SWIGLANG=python
+# Sets up environment for using various target languages
+# For Github Actions where the environment is not preserved between steps
+set -e # exit on failure (same as -o errexit)
+
+case "$SWIGLANG" in
+	"javascript")
+		case "$ENGINE" in
+			"node")
+				export NVM_DIR="$HOME/.nvm"
+				[ -s "$NVM_DIR/nvm.sh" ] && source "$NVM_DIR/nvm.sh"
+				nvm use ${VER}
+				;;
+			*)      ;;
+		esac
+		;;
+	"ruby")
+		if ! command -v rvm; then
+			set +x
+			source $HOME/.rvm/scripts/rvm
+			set -x
+		fi
+		;;
+	*)	;;
+esac

Tools/CI-linux-install.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# expected to be called from elsewhere with certain variables set
+# Expected to be called from elsewhere with certain variables set
 # e.g. RETRY=travis-retry SWIGLANG=python GCC=7
 set -e # exit on failure (same as -o errexit)