obs2ioda-v2.x replaces output files for sub-hourly HSD data

[mrixlam]

It has recently been found that the obs2ioda-v2.x uses the following naming convention for output files generated for HSD data:
"ahi_himawari8_obs_yyyymmddhh.h5"

Therefore, the use of sub-hourly HSD data will lead to automatic file replacement. For example, if we use obs2ioda-v2.x to convert HSD data for the following times:

HS_H08_20180101_0000_Bxx_FLDK_R20_S0101.DAT
HS_H08_20180101_0010_Bxx_FLDK_R20_S0101.DAT
HS_H08_20180101_0020_Bxx_FLDK_R20_S0101.DAT
HS_H08_20180101_0030_Bxx_FLDK_R20_S0101.DAT
HS_H08_20180101_0040_Bxx_FLDK_R20_S0101.DAT
HS_H08_20180101_0050_Bxx_FLDK_R20_S0101.DAT

all the output files will have the same output filename: "ahi_himawari8_obs_2018010100.h5". If they were written in the same directory, output files for 00:00, 00:10, 00:20, 00:30, and 00:40 will be replaced by the output file at 00:50.