Refactored SuSEFirewallServices

- Mostly to throw an exception if required service is not found, till now
  it used to be just logged and thus was hard to find out what was wrong
- bnc#867377
Added testcase for SuSEfirewallService
Using the new exception SuSEFirewalServiceNotFound in CWMFirewallInterfaces
Changes required by pull-request reviewers
Adapted testsuite

- It did not test anything and it's impossible to check
  the exception in old-fashioned Yast code
Changes file entry and a new version
Merge pull request #195 from kobliha/firewall_throws_exception

Refactoring SuSEFirewallService - Firewall throws exception