Prevent some random build failures when connectivity fails, by callin…

…g travis_retry which retries up to 3 times

https://travis-ci.org/piwik/piwik/jobs/23570274
https://travis-ci.org/piwik/piwik/jobs/23912462
http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries/

tests/angularjs/scripts/install-ubuntu.sh

@@ -1,3 +1,26 @@
+# Prevent random build failures by retrying 3 times
+# Source: https://github.com/travis-ci/travis-build/blob/fc4ae8a2ffa1f2b3a2f62533bbc4f8a9be19a8ae/lib/travis/build/script/templates/header.sh#L104
+travis_retry() {
+  local result=0
+  local count=1
+  while [ $count -le 3 ]; do
+    [ $result -ne 0 ] && {
+      echo -e "\n${RED}The command \"$@\" failed. Retrying, $count of 3.${RESET}\n" >&2
+    }
+    "$@"
+    result=$?
+    [ $result -eq 0 ] && break
+count=$(($count + 1))
+    sleep 1
+  done
+
+  [ $count -eq 3 ] && {
+    echo "\n${RED}The command \"$@\" failed 3 times.${RESET}\n" >&2
+  }
+
+  return $result
+}
+
 DIR=`dirname $0`
 cd $DIR
 travis_retry sudo apt-get -qq install python-software-properties