Seperate checking dns servers out into a function

The curent check only tests the first server in the list, if more than one server is specified we should only be concerned if none are available.
This change does not change the current functionality, but is a stepping stone towards a fix for the above.
Check all servers listed

Continue if at least one works, abort if none work.

Fixes #147.
Change project name to something meaningful
Increase purity

$check gets overwritten in the if-else block below, so doesn't need an initial value.
Make testservers an array

This way we can get rid of the if-else block which calls check_dns_servers.
As suggested by @msmark, thanks!
Merge branch 'master' of github.com:quattor/configuration-modules-core into resolver-graceful-failure

Conflicts:
	ncm-resolver/pom.xml
Merge pull request #282 from jrha/resolver-graceful-failure

ncm-resolver: Check all servers listed in configuration