Add flexibility to the iOS UIExplorer test script

Summary:
Add more flexibility to the iOS UIExplorer test scripts:
- support environments without `xcpretty` installed
- support custom xcode destination argument

Initial PR is based on the last git commit which passed on Travis today (2a92b52) in order to test Travis build.

I'll rebase to latest, in order to fix merge conflicts, before merging.

**Test plan (required)**

Make sure tests pass on Travis.
Closes https://github.com/facebook/react-native/pull/7982

Differential Revision: D3404574

Pulled By: avaly

fbshipit-source-id: 48aabd81fba67d482af46728a9c3975842f03060

scripts/objc-test.sh

@@ -5,8 +5,6 @@ set -e
 SCRIPTS=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
 ROOT=$(dirname $SCRIPTS)
 
-export REACT_PACKAGER_LOG="$ROOT/server.log"
-
 cd $ROOT
 
 function cleanup {
@@ -17,17 +15,29 @@ function cleanup {
   then
     WATCHMAN_LOGS=/usr/local/Cellar/watchman/3.1/var/run/watchman/$USER.log
     [ -f $WATCHMAN_LOGS ] && cat $WATCHMAN_LOGS
-
-    [ -f $REACT_PACKAGER_LOG ] && cat $REACT_PACKAGER_LOG
   fi
 }
 trap cleanup EXIT
 
+if [ -z "$XCODE_DESTINATION" ]; then
+  XCODE_DESTINATION="platform=iOS Simulator,name=iPhone 5,OS=9.3"
+fi
+
+# Support for environments without xcpretty installed
+set +e
+OUTPUT_TOOL=$(which xcpretty)
+set -e
+if [ -z "$OUTPUT_TOOL" ]; then
+  OUTPUT_TOOL="sed"
+fi
+
 # TODO: We use xcodebuild because xctool would stall when collecting info about
 # the tests before running them. Switch back when this issue with xctool has
 # been resolved.
 xcodebuild \
   -project Examples/UIExplorer/UIExplorer.xcodeproj \
-  -scheme UIExplorer -sdk iphonesimulator -destination 'platform=iOS Simulator,name=iPhone 5,OS=9.3' \
+  -scheme UIExplorer \
+  -sdk iphonesimulator \
+  -destination "$XCODE_DESTINATION" \
   test \
-| xcpretty && exit ${PIPESTATUS[0]}
+  | $OUTPUT_TOOL && exit ${PIPESTATUS[0]}