add Eternus mapping

[zhilong-xu]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

Release note:

[codecov]

Codecov Report

Merging #493 (b83010e) into eternus-mapping (122c928) will increase coverage by 0.46%.
The diff coverage is 92.01%.

@@                 Coverage Diff                 @@
##           eternus-mapping     #493      +/-   ##
===================================================
+ Coverage            70.59%   71.05%   +0.46%     
===================================================
  Files                  180      180              
  Lines                18648    19091     +443     
  Branches              2750     2843      +93     
===================================================
+ Hits                 13165    13566     +401     
- Misses                4644     4660      +16     
- Partials               839      865      +26     

Impacted Files	Coverage Δ
delfin/drivers/fujitsu/eternus/eternus_stor.py	88.39% <90.33%> (+2.09%)	⬆️
delfin/drivers/fujitsu/eternus/cli_handler.py	84.21% <100.00%> (ø)
delfin/drivers/fujitsu/eternus/consts.py	100.00% <100.00%> (ø)
delfin/drivers/fake_storage/__init__.py	94.40% <0.00%> (-1.02%)	⬇️
delfin/common/constants.py	100.00% <0.00%> (ø)
delfin/context.py	74.50% <0.00%> (+0.50%)	⬆️