Tolerate an already existing user

If a user already exists, catch this error so that we don't exit.

Change-Id: Iedc3a78d7a13680e6fb813fcce359fd116d6916f

setup.sh

diff --git a/setup.sh b/setup.sh
index a63baf8..a064d6b 100755
--- a/setup.sh
+++ b/setup.sh
@@ -42,7 +42,7 @@
 # Install the needed packages and setup the environment
 apt-get install -y gcc openjdk-7-jdk ant maven zip
 echo "0 0 * * * /usr/pb/setup.sh build >> /var/log/pb.log" | crontab -
-adduser --uid 1337 --disabled-password --gecos ,,, worker
+adduser --uid 1337 --disabled-password --gecos ,,, worker || true
 
 
 # Kick off a build if requested