add os_type

[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 #521 (edb1ca1) into pure-mapping (9bcae97) will increase coverage by 0.19%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           pure-mapping     #521      +/-   ##
================================================
+ Coverage         70.67%   70.87%   +0.19%     
================================================
  Files               180      180              
  Lines             18737    19259     +522     
  Branches           2764     2899     +135     
================================================
+ Hits              13243    13650     +407     
- Misses             4648     4748     +100     
- Partials            846      861      +15     

Impacted Files	Coverage Δ
delfin/drivers/pure/flasharray/consts.py	100.00% <ø> (ø)
delfin/drivers/driver.py	60.97% <0.00%> (-0.79%)	⬇️
delfin/common/constants.py	100.00% <0.00%> (ø)
delfin/drivers/hitachi/vsp/vsp_stor.py	70.52% <0.00%> (+0.22%)	⬆️
delfin/drivers/dell_emc/vmax/vmax.py	81.90% <0.00%> (+1.34%)	⬆️
delfin/drivers/fake_storage/__init__.py	95.35% <0.00%> (+1.71%)	⬆️
delfin/drivers/dell_emc/vmax/rest.py	47.55% <0.00%> (+3.36%)	⬆️
delfin/drivers/dell_emc/vmax/client.py	79.32% <0.00%> (+5.97%)	⬆️