Prepend missing MetricFu namespace to ReekHotspot

Until https://github.com/travis-ci/travis-ci/issues/2220 is fixed

Also see https://github.com/Shopify/active_merchant/pull/1150

It appears rbx is similarly broken
https://github.com/travis-ci/travis-ci/issues/2230
SimpleCov coverage saving for rake task
Start SimpleCov before loading any metric_fu, then set formatter

Otherwise, metric_fu code will be loaded before SimpleCov turns
Coverage on and it will not be tracked
More SimpleCov groups
Test fix actual fix for #153; ignore lines SimpleCov ignores

Will break old RCov behavior where a file is that is loaded, but
no lines executed, will have a coverage percentage.  Under the
new rubric, it will be 0.0, which really is more correct.

Since we've already removed support for running via RCov, this
won't be a problem.
Break old RCov behavior in favor of SimpleCov, see previous commit
Fixes #153; Coverage reports now behave like SimpleCov
Set JRUBY_OPTS="-Xcli.debug=true" for SimpleCov

Modified per
http://docs.travis-ci.com/user/ci-environment/#Environment-variables

h/t @enebo https://twitter.com/tom_enebo/status/462289024107814914

Failure message was
home/travis/build/metricfu/metric_fu/gemfiles/vendor/bundle/jruby/1.9/gems/simplecov-0.8.2/lib/simplecov.rb:31 warning: tracing (e.g. set_trace_func) will not capture all events without --debug flag

SimpleCov::Formatter::MetricFu calculates the same coverage from an RCov report as from SimpleCov
     Failure/Error: expect(source_file.coverage.count).to eq(covered_lines_from_rcov_text.count)

       expected: 11
            got: 8

       (compared using ==)
     # /home/travis/build/metricfu/metric_fu/spec/metric_fu/metrics/rcov/simplecov_formatter_spec.rb:52:in `(root)'
     # /home/travis/build/metricfu/metric_fu/spec/support/timeout.rb:6:in `(root)'