Omitted tests should be reported as <skipped>

[MariuszCwikla]

Following test

def test_omit    
  omit 'omitted'
end

is reported as

<testcase name="test_omit" time="0.000373181" assertions="0">
    <failure type="Test::Unit::Omission" message="omitted">...</failure>
</testcase>

but it should be reported as <skipped> instead of <failure>

Simple fix is to set up skipped flag ci-reporter's TestCase which was not used in ci_reporter_test_unit yet

[MariuszCwikla]

@nicksieger @shepmaster any update regarding this?
Please check also #12