issues: 216329175

When loading from NetCDF, Dataset.attrs often has a few long strings, which may even have embedded newlines (eg a multi-paragraph summary or references section). It's lovely that these are available, but they tend to make the repr very long and poorly formatted - to the point that many Jupyter notebooks begin by discarding the attrs, which makes it rather pointless to store or display metadata at all!

Given that these values are already truncated at 500 characters (including the indicative ..., but not the start point), I propose that they should instead be truncated to 80 characters including the indentation and key (as values are). For the sake of pretty-printing, this should also replace newlines or tabs with spaces and truncate early if an empty line is encountered.

Another solution would be add appropriate indentation following newlines or wrapping, so that the structure remains clear. However, I think that it is better to print a fairly minimal representation of the metadata by default.

```

xr.open_dataset('http://dapds00.nci.org.au/thredds/dodsC/uc0/rs0_dev/20170215-stacked_sample/LS7_ETM_NBART_3577_15_-40.ncml')

<xarray.Dataset> Dimensions: (time: 246, x: 4000, y: 4000) Coordinates: * y (y) float64 -3.9e+06 -3.9e+06 -3.9e+06 -3.9e+06 -3.9e+06 ... * x (x) float64 1.5e+06 1.5e+06 1.5e+06 1.5e+06 1.5e+06 1.5e+06 ... * time (time) datetime64[ns] 1999-07-16T23:49:39 1999-07-25T23:43:07 ... Data variables: crs int32 ... blue (time, y, x) float64 ... green (time, y, x) float64 ... red (time, y, x) float64 ... nir (time, y, x) float64 ... swir1 (time, y, x) float64 ... swir2 (time, y, x) float64 ... Attributes: date_created: 2017-03-07T11:57:26.511217 Conventions: CF-1.6, ACDD-1.3 history: 2017-03-07T11:57:26.511307+11:00 adh547 datacube-ncml (1.2.2+23.gd1f3512.dirty) ls7_nbart_albers.yaml, 1.0.6a, /short/v10/datacube/002/LS7_ETM_NBART/LS7_ETM_NBART_3577_15_-40.ncml, (15, -40) # Created NCML file to aggregate multiple NetCDF files along the time dimension geospatial_bounds: POLYGON ((148.49626113888138 -34.828378308133452,148.638689676063308 -35.720318326735864,149.734176111491877 -35.599556747691196,149.582601578289143 -34.708911907843387,148.49626113888138 -34.828378308133452)) geospatial_bounds_crs: EPSG:4326 geospatial_lat_min: -35.7203183267 geospatial_lat_max: -34.7089119078 geospatial_lat_units: degrees_north geospatial_lon_min: 148.496261139 geospatial_lon_max: 149.734176111 geospatial_lon_units: degrees_east comment: - Ground Control Points (GCP): new GCP chips released by USGS in Dec 2015 are used for re-processing - Geometric QA: each product undergoes geometric assessment and the assessment result will be recorded within v2 AGDC for filtering/masking purposes. - Processing parameter settings: the minimum number of GCPs for Ortho-rectified product generation has been reduced from 30 to 10. - DEM: 1 second SRTM DSM is used for Ortho-rectification. - Updated Calibration Parameter File (CPF): the latest/cu... product_suite: Surface Reflectance NBAR+T 25m publisher_email: earth.observation@ga.gov.au keywords_vocabulary: GCMD product_version: 2 cdm_data_type: Grid references: - Berk, A., Anderson, G.P., Acharya, P.K., Hoke, M.L., Chetwynd, J.H., Bernstein, L.S., Shettle, E.P., Matthew, M.W., and Adler-Golden, S.M. (2003) Modtran 4 Version 3 Revision 1 User s manual. Airforce Research Laboratory, Hanscom, MA, USA. - Chander, G., Markham, B.L., and Helder, D.L. (2009) Summary of current radiometric calibration coefficients for Landsat MSS, TM, ETM+, and EO-1 ALI sensors. Remote Sensing of Environment 113, 893-903. - Edberg, R., and Oliver, S. (2013) Projection-Indep... platform: LANDSAT-7 keywords: AU/GA,NASA/GSFC/SED/ESD/LANDSAT,REFLECTANCE,ETM+,TM,OLI,EARTH SCIENCE publisher_name: Section Leader, Operations Section, NEMO, Geoscience Australia institution: Commonwealth of Australia (Geoscience Australia) acknowledgment: Landsat data is provided by the United States Geological Survey (USGS) through direct reception of the data at Geoscience Australias satellite reception facility or download. license: CC BY Attribution 4.0 International License title: Surface Reflectance NBAR+T 25 v2 summary: Surface Reflectance (SR) is a suite of Earth Observation (EO) products from GA. The SR product suite provides standardised optical surface reflectance datasets using robust physical models to correct for variations in image radiance values due to atmospheric properties, and sun and sensor geometry. The resulting stack of surface reflectance grids are consistent over space and time which is instrumental in identifying and quantifying environmental change. SR is based on radiance data from the... instrument: ETM source: LANDSAT 7 ETM+ surface observation publisher_url: http://www.ga.gov.au ```