Improved brokers.py output

These changes improve the output of brokers.py when it is run as a standalone script to fetch lists of brokers. The output now looks like the following:

== SSL production brokers ==
msg.cro-ngi.hr:6162
egi-2.msg.cern.ch:6162
egi-1.msg.cern.ch:6162
broker.afroditi.hellasgrid.gr:6162

== Production brokers ==
msg.cro-ngi.hr:6163
egi-2.msg.cern.ch:6163
egi-1.msg.cern.ch:6163
broker.afroditi.hellasgrid.gr:6163

== SSL test brokers ==
msg-test.cro-ngi.hr:6162
test-msg02.afroditi.hellasgrid.gr:6162

== Test brokers ==
msg-test.cro-ngi.hr:6163
test-msg02.afroditi.hellasgrid.gr:6163