unity add rest retry time

[tanjiangyu-ghca]

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 #523 (98743cc) into unity_1123 (579d8c0) will decrease coverage by 0.01%.
The diff coverage is 64.28%.

@@              Coverage Diff               @@
##           unity_1123     #523      +/-   ##
==============================================
- Coverage       70.64%   70.62%   -0.02%     
==============================================
  Files             180      180              
  Lines           18853    18862       +9     
  Branches         2801     2802       +1     
==============================================
+ Hits            13318    13322       +4     
- Misses           4668     4674       +6     
+ Partials          867      866       -1     

Impacted Files	Coverage Δ
delfin/drivers/dell_emc/unity/rest_handler.py	46.99% <40.00%> (-1.33%)	⬇️
delfin/drivers/dell_emc/unity/unity.py	70.00% <70.96%> (-0.38%)	⬇️
delfin/drivers/dell_emc/unity/consts.py	100.00% <100.00%> (ø)
delfin/drivers/fake_storage/__init__.py	95.16% <0.00%> (+0.76%)	⬆️