hdf5 files do not save runinfo.measured

[mplilly4395]

runinfo.measured is important for existing plot commands like PlotGenerator(). When you use the expt created in a jupyter notebook, the measured list is present. If you use ps.load_experiment(), measured is an empty list.

In checking on this problem,

1. save_metadata() runs recursive_to_dict() and json.dumps()
2. recursive_to_dict() makes a dictionary with measured and the list is correct at this point
3. directly checking the hdf5 file runinfo attr: f.attrs['runinfo'], measured is an empty list.

[i-am-mounce]

Let's add this functionality to load_experiment

[mplilly4395]

reason: metadata is saved before the experiment begins. The measured list is populated after the first data point, so it is empty when the metadata is saved.