Add error handling to install_rally.sh

Use the 'set -e' command inside the script to enforce it to stop
execution and exit with an error status code whenever one of its
commands fail.
Currently it is a bit experimental, so any test report will be
appreciated.

Change-Id: I0a084e89e6387c5e4fd28c62369aa377212947c3

install_rally.sh

@@ -9,6 +9,7 @@
 # programs already installed:
 # -> Python 2.6 or Python 2.7
 
+set -e
 
 err() {
   echo "${0##*/}: $@" >&2