Squashed 0944d8a (check_timeout) into one commit:

coSimplify and expand tests, adding tests for:
* timeout conditions
* unreachable hosts and routes
* open and unused ports

Added test/setup_ubuntu.bash to setup unreachable host, route,
and confirm we can still use telstra.com as a black hole
for pings and tests for ports 7, 22 and 1001

Refactored tests to line up with existing example in external

Add extra rvm versions;
Add IGNORE_HTTP_PING_DOES_NOT_WAITS_FOR_RESPONSE_BUG and
IGNORE_HTTP_PING_DOES_NOT_TIMEOUT_BUG to test those bugs with
failure allowed;

Reorganise .travis.yml to make intent clearer

Speed up timeout tests

Give more details on failing tests
Change UNREACHABLE_HOST to using a script to try and find an unreachable host (using iptables doesn't work for host unreachable);
Don't enforce that icmp pings have to wait if they discover network unreachable early;
Merge branch 'extra_timeout_and_unreachable_tests' into fix_ICMP_ENETUNREACH_BUG

Conflicts:
	.travis.yml
	test/test_net_ping_external.rb