idle: Add parser for cpu_idle events

[JaviMerino]

Please add the trace.dat instead of the trace.txt. The existing trace.txts make it hard to implement #210 (I had the code but I had to change the existing trace.txts as trace.dat and I never got time to do it). Let's not increase the number of them by having them in binary form. You will have to annotate TestCpuIdle with:

@unittest.skipUnless(utils_tests.trace_cmd_installed(),
                     "trace-cmd not installed")

[JaviMerino]

travis says that this breaks the tests because tests/trace_empty.txt is no longer "empty". Can you remove the cpu_idle events in there to avoid breaking the testsuite?

[bjackman]

Pushed a new version using assert_series_equal, unfortunately (?) you also have to explicitly do assert_index_equal too, assert_series_equal only seems to check the values. check_exact=True makes assert_series_equal check the index too.

[JaviMerino]

great, thanks! :heart: