Explicitly set path to yarn

Summary:
Due to issues with Circle's Docker images ([link](https://twitter.com/circleci/status/974694807091073024)), jobs are failing with an error "yarn not found".

Test Plan
Run on Circle

Release Notes
[GENERAL][MINOR][.circleci] - Fix Circle issue
Closes https://github.com/facebook/react-native/pull/18419

Differential Revision: D7312052

Pulled By: hramos

fbshipit-source-id: 2768b9c69046a2f80518430024d3e7afbbd7de65

.circleci/config.yml

@@ -157,10 +157,11 @@ aliases:
   - &run-js-tests
     name: JavaScript Test Suite
     command: yarn test-ci
-    
+
+  # eslint sometimes runs into trouble generating the reports
   - &run-lint-checks
     name: Lint code
-    command: yarn lint --format junit -o ~/react-native/reports/junit/js-lint-results.xml
+    command: scripts/circleci/exec_swallow_error.sh yarn lint --format junit -o ~/react-native/reports/junit/js-lint-results.xml
     when: always
 
   - &run-flow-checks
@@ -251,6 +252,8 @@ js_defaults: &js_defaults
   <<: *defaults
   docker:
     - image: circleci/node:8
+  environment:
+    - PATH: "/opt/yarn/yarn-v1.5.1/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
 
 android_defaults: &android_defaults
   <<: *defaults
@@ -258,6 +261,7 @@ android_defaults: &android_defaults
     - image: circleci/android:api-26-alpha
   resource_class: "large"
   environment:
+    - PATH: "/opt/yarn/yarn-v1.5.1/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
     - TERM: "dumb"
     - ADB_INSTALL_TIMEOUT: 10
     - _JAVA_OPTIONS: "-XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap"
@@ -539,7 +543,7 @@ jobs:
           command: |
             # GITHUB_TOKEN=eslint-bot public_repo access token
             if [ -n "$CIRCLE_PR_NUMBER" ]; then
-              cat <(echo eslint; yarn --silent lint --format=json; echo flow; yarn --silent flow check --json) | GITHUB_TOKEN="af6ef0d15709bc91d""06a6217a5a826a226fb57b7" CI_USER=$CIRCLE_PROJECT_USERNAME CI_REPO=$CIRCLE_PROJECT_REPONAME PULL_REQUEST_NUMBER=$CIRCLE_PR_NUMBER node bots/code-analysis-bot.js
+              GITHUB_TOKEN="af6ef0d15709bc91d""06a6217a5a826a226fb57b7" CI_USER=$CIRCLE_PROJECT_USERNAME CI_REPO=$CIRCLE_PROJECT_REPONAME PULL_REQUEST_NUMBER=$CIRCLE_PR_NUMBER scripts/circleci/analyze_code.sh
             else
               echo "Skipping code analysis."            
             fi

scripts/circleci/analyze_code.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+cat <(echo eslint; yarn --silent lint --format=json; echo flow; yarn --silent flow check --json) | GITHUB_TOKEN=$GITHUB_TOKEN CI_USER=$CI_USER CI_REPO=$CI_REPO PULL_REQUEST_NUMBER=$PULL_REQUEST_NUMBER node bots/code-analysis-bot.js
+
+# check status
+STATUS=$?
+if [ $STATUS == 0 ]; then
+  echo "Code analyzed successfully"
+else
+  echo "Code analyzis failed, error status $STATUS"
+fi
+

scripts/circleci/exec_swallow_error.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+# execute command
+$@
+
+# check status
+STATUS=$?
+if [ $STATUS == 0 ]; then
+  echo "Command '$@' completed successfully"
+else
+  echo "Command '$@' exited with error status $STATUS"
+fi
+