fix rust error when choose a non-default version. (#111)

port of https://github.com/microsoft/vscode-dev-containers/pull/1592

src/rust/devcontainer-feature.json

 {
     "id": "rust",
-    "version": "1.0.2",
+    "version": "1.0.3",
     "name": "Rust",
     "description": "Installs Rust, common Rust utilities, and their required dependencies",
     "options": {

src/rust/install.sh

@@ -179,8 +179,8 @@ else
             apt-get -y install --no-install-recommends git
         fi
 
-        echo ${RUST_VERSION} | grep -q "nightly"
-        is_nightly=$?
+        is_nightly=0
+        echo ${RUST_VERSION} | grep -q "nightly" || is_nightly=$?
         if [ $is_nightly = 0 ]; then
             check_nightly_version_formatting RUST_VERSION
         else

test-scenarios/rust_at_pinned_version.sh

+#!/bin/bash
+
+set -e
+
+# Optional: Import test library
+source dev-container-features-test-lib
+
+# Definition specific tests
+check "cargo version" cargo  --version
+check "rustc version" rustc  --version
+check "correct rust version" rustc  --version | grep 1.62.0
+
+
+# Report result
+reportResults
\ No newline at end of file

test-scenarios/scenarios.json

@@ -92,6 +92,14 @@
             }
         }
     },
+    "rust_at_pinned_version": {
+        "image": "ubuntu:focal",
+        "features": {
+            "rust": {
+                "version": "1.62.0"
+            }
+        }
+    },
     "install_cudnn_nvxt": {
         "image": "debian",
         "features": {