Fix testBundleURL in react-native-oss-ios

Summary:
The react-native-oss-ios job has been failing when testBundleURL gets a local filesystem URL instead of a packager URL.

Setting CI_USE_PACKAGER allows us to force the test to use the packager.

Changelog:
[Internal]

Reviewed By: mmmulani

Differential Revision: D19105213

fbshipit-source-id: a58089bf278ca0f08dd3f4df94e9fe8ce9a63376

RNTester/RNTesterPods.xcodeproj/xcshareddata/xcschemes/RNTesterUnitTests.xcscheme

@@ -77,6 +77,13 @@
             ReferencedContainer = "container:RNTesterPods.xcodeproj">
          </BuildableReference>
       </MacroExpansion>
+      <EnvironmentVariables>
+         <EnvironmentVariable
+            key = "CI_USE_PACKAGER"
+            value = "1"
+            isEnabled = "YES">
+         </EnvironmentVariable>
+      </EnvironmentVariables>
       <AdditionalOptions>
       </AdditionalOptions>
    </TestAction>