Fix errors in OSN instructions

[rabernat]

Some updates in response to the problems uncovered by @neerajabhamidipati in ocean-eddy-cpt/NeverWorld2#3.

[rabernat]

Other things:

• add --recursive option
• add ls to verify
• pip install awscli-plugin-endpoint
• plugin in config

[neerajabhamidipati]

Also add the following code snippet by @rabernat to the steps if decode_times=False when reading netcdf files:

for var in ds.variables:
    # fix wrong calendar encoding
    if ds[var].attrs.get('calendar') == 'THIRTY_DAY_MONTHS':
        ds[var].attrs['calendar'] = '360_day'
    # fix missing calendar encoding
    elif ds[var].dims == ('time',) and ds[var].attrs.get('units', '').startswith('days'):
        ds[var].attrs['calendar'] = '360_day'
ds = xr.decode_cf(ds)