netcdf preserve file metadata

[Dimitar Misev]

When importing netcdf files the metadata should be preserved precisely, and not converted to string. For example in eobstest

	short tg(time, latitude, longitude) ;
		tg:long_name = "mean temperature" ;
		tg:units = "Celsius" ;
		tg:standard_name = "air_temperature" ;
		tg:_FillValue = -9999s ;
		tg:scale_factor = 0.01f ;

_FillValue and scale_factor should be kept as short and float values, and should not be converted to string.

Furthermore, some metadata is not preserved at all (unix, E, N) + mixed up with global/local metadata?

Input file metadata (in wcps_irregular_time_nc):

netcdf irr_time {
dimensions:
	unix = 15 ;
	N = 1 ;
	E = 1 ;
variables:
	short band_1(unix, N, E) ;
		band_1:valid_min = -32768s ;
		band_1:valid_max = 32767s ;
		band_1:units = "10^0" ;
	short band_2(unix, N, E) ;
		band_2:valid_min = -32768s ;
		band_2:valid_max = 32767s ;
		band_2:units = "10^0" ;
	short band_3(unix, N, E) ;
		band_3:valid_min = -32768s ;
		band_3:valid_max = 32767s ;
		band_3:units = "10^0" ;
	short band_4(unix, N, E) ;
		band_4:valid_min = -32768s ;
		band_4:valid_max = 32767s ;
		band_4:units = "10^0" ;
	short band_5(unix, N, E) ;
		band_5:valid_min = -32768s ;
		band_5:valid_max = 32767s ;
		band_5:units = "10^0" ;
	short band_6(unix, N, E) ;
		band_6:valid_min = -32768s ;
		band_6:valid_max = 32767s ;
		band_6:units = "10^0" ;
	short band_7(unix, N, E) ;
		band_7:valid_min = -32768s ;
		band_7:valid_max = 32767s ;
		band_7:units = "10^0" ;
	double E(E) ;
		E:axis = "X" ;
		E:standard_name = "longitude" ;
		E:units = "m" ;
	double N(N) ;
		N:axis = "Y" ;
		N:standard_name = "latitude" ;
		N:units = "m" ;
	double unix(unix) ;
		unix:axis = "T" ;
		unix:standard_name = "unix" ;
		unix:units = "d" ;

// global attributes:
		:Conventions = "CF-1.6, ACDD-1.3" ;
		:date_created = "2016-04-12T11:11:42.114427" ;
		:history = "NetCDF-CF file created by datacube version \'1.0.2\' at 20160412." ;
		:product_version = "0.0.0" ;
		:source = "This data is a reprojection and retile of Landsat surface reflectance scene data." ;
		:summary = "These files are experimental, short lived, and the format will change." ;
		:title = "Experimental Data files From the Australian Geoscience Data Cube - DO NOT USE" ;
}

output file metadata:

netcdf \153-irr_cube_3D_time_irregular {
dimensions:
	unix = 15 ;
	N = 1 ;
	E = 1 ;
variables:
	short band_1(unix, N, E) ;
		band_1:valid_min = -32768s ;
		band_1:valid_max = 32767s ;
		band_1:missing_value = -999s ;
		band_1:_FillValue = -999s ;
		band_1:description = "Nadir BRDF Adjusted Reflectance 0.43-0.45 microns (Coastal Aerosol)" ;
		band_1:product_version = "0.0.0" ;
		band_1:test_empty_attribute = "" ;
		band_1:units = "10^0" ;
	short band_2(unix, N, E) ;
		band_2:valid_min = -32768s ;
		band_2:valid_max = 32767s ;
		band_2:missing_value = -999s ;
		band_2:_FillValue = -999s ;
		band_2:units = "10^0" ;
	short band_3(unix, N, E) ;
		band_3:valid_min = -32768s ;
		band_3:valid_max = 32767s ;
		band_3:missing_value = -999s ;
		band_3:_FillValue = -999s ;
		band_3:units = "10^0" ;
	short band_4(unix, N, E) ;
		band_4:valid_min = -32768s ;
		band_4:valid_max = 32767s ;
		band_4:missing_value = -999s ;
		band_4:_FillValue = -999s ;
		band_4:units = "10^0" ;
	short band_5(unix, N, E) ;
		band_5:valid_min = -32768s ;
		band_5:valid_max = 32767s ;
		band_5:missing_value = -999s ;
		band_5:_FillValue = -999s ;
		band_5:units = "10^0" ;
	short band_6(unix, N, E) ;
		band_6:valid_min = -32768s ;
		band_6:valid_max = 32767s ;
		band_6:missing_value = -999s ;
		band_6:_FillValue = -999s ;
		band_6:units = "10^0" ;
	short band_7(unix, N, E) ;
		band_7:valid_min = -32768s ;
		band_7:valid_max = 32767s ;
		band_7:missing_value = -999s ;
		band_7:_FillValue = -999s ;
		band_7:Conventions = "CF-1.6, ACDD-1.3" ;
		band_7:date_created = "2016-04-12T11:11:42.114427" ;
		band_7:units = "10^0" ;
	double E(E) ;
	double N(N) ;
	double unix(unix) ;
		unix:directPositions = "-1000012.5" ;
		unix:max = "1387331687.45" ;
		unix:min = "1370137750.3699999" ;

// global attributes:
		:Conventions = "CF-1.6, ACDD-1.3" ;
		:date_created = "2016-04-12T11:11:42.114427" ;
		:history = "NetCDF-CF file created by datacube version \'1.0.2\' at 20160412." ;
		:product_version = "0.0.0" ;
		:source = "This data is a reprojection and retile of Landsat surface reflectance scene data." ;
		:summary = "These files are experimental, short lived, and the format will change." ;
		:test_empty_attribute = "" ;
		:title = "Experimental Data files From the Australian Geoscience Data Cube - DO NOT USE" ;