Modify naming and attributes of time variables on history files to be consistent with other CESM components

[phillips-ad]

These changes are being requested to improve the ease-of-access of CESM data and to normalize the look of the metadata across CESM components. See ESCOMP/CESM#194 and especially the google doc referenced from ESCOMP/CESM#194 (comment)

Current CICE time array output:

float time(time) ;
	time:long_name = "model time" ;
	time:units = "days since 0001-01-01 00:00:00" ;
	time:calendar = "noleap" ;
	time:bounds = "time_bounds" ;
float time_bounds(time, d2) ;
	time_bounds:long_name = "boundaries for time-averaging interval" ;
	time_bounds:units = "days since 0001-01-01 00:00:00" ;

Proposed CICE time array output:

double time(time) ;
	time:long_name = "time" ;
	time:units = "days since 0001-01-01 00:00:00" ;
	time:calendar = "noleap" ;
	time:bounds = "time_bounds" ;
double time_bounds(time, nbnd) ;
	time_bounds:long_name = "time interval endpoints" ;
	time_bounds:units = "days since 0001-01-01 00:00:00" ;
        time_bounds:calendar = "noleap" ;

Changes made: Change time/time_bounds to type double, add calendar attribute to time_bounds, change 2nd dimension name of time_bounds to nbnd, change time@long_name to “time”, change time_bounds@long_name to "time interval endpoints"

@billsacks @phillips-ad @strandwg are filing similar issues for each component.

[dabail10]

Resolved in cice6_4_1_8.