moving perl based unit tests to retire
new config parameter: CVMFS_DNS_SERVER
improving stopwatch
TEST: unreachable DNS failure
remove DNS related configuration functions from common test functions
add a python script that opens a [TCP|UDP] socket on a specified port and stays silent on connection
remove iptables configuration from test_functions
add a shell function to test_functions that opens a silent UDP|TCP port
TEST: DNS server is available but doesn't answer
Merge pull request #198 from reneme/failover_tests

TEST: two new test cases related to DNS outages