Fix syntax error.

change $identity_output -> identity output since shell script crashed at this line.
No password is printed. but just to be safe, also hide the output from set-key-partition-list. redirect it to /dev/null

Change-Id: I0ebf75fe7ac6321e9fe3191d3a31f8c44f50525b
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/56747
Reviewed-by: Christopher Fujino <fujino@google.com>
Commit-Queue: Xilai Zhang <xilaizhang@google.com>
diff --git a/recipe_modules/signing/resources/setup_keychain.sh b/recipe_modules/signing/resources/setup_keychain.sh
index b7906c1..18d3852 100644
--- a/recipe_modules/signing/resources/setup_keychain.sh
+++ b/recipe_modules/signing/resources/setup_keychain.sh
@@ -47,8 +47,8 @@
 while [ $attempt -lt 3 ]; do
    echo "attempt #$attempt"
    /usr/bin/security import $P12_SUFFIX_FILEPATH -k build.keychain -P $RAW_PASSWORD -T $CODESIGN_PATH -T /usr/bin/codesign
-   /usr/bin/security set-key-partition-list -S apple-tool:,apple:,codesign: -s -k '' build.keychain
-   $IDENTITY_OUTPUT=$(/usr/bin/security find-identity -v build.keychain)
+   /usr/bin/security set-key-partition-list -S apple-tool:,apple:,codesign: -s -k '' build.keychain >/dev/null 2>&1
+   IDENTITY_OUTPUT=$(/usr/bin/security find-identity -v build.keychain)
    echo "$IDENTITY_OUTPUT"
    if echo "$IDENTITY_OUTPUT" | grep 'FLUTTER.IO LLC'; then
      exit 0