Bug fix about alarm mangement and refactor some classes and constants.

[littlehotcx]

What this PR does / why we need it:

1. Bug fix about alarm management.
2. Refactor some classes and constants.
   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 #912 (8e4d0f5) into master (1422a00) will increase coverage by 0.00%.
The diff coverage is 82.16%.

@@           Coverage Diff           @@
##           master     #912   +/-   ##
=======================================
  Coverage   71.12%   71.13%           
=======================================
  Files         182      182           
  Lines       21889    21899   +10     
  Branches     3346     3340    -6     
=======================================
+ Hits        15568    15577    +9     
+ Misses       5268     5266    -2     
- Partials     1053     1056    +3     

Impacted Files	Coverage Δ
delfin/api/v1/storages.py	75.62% <0.00%> (ø)
delfin/drivers/utils/rest_client.py	39.43% <0.00%> (+0.54%)	⬆️
delfin/alert_manager/trap_receiver.py	72.89% <67.30%> (-3.58%)	⬇️
delfin/alert_manager/snmp_validator.py	76.31% <82.60%> (-1.81%)	⬇️
delfin/task_manager/tasks/resources.py	87.80% <93.75%> (+1.96%)	⬆️
delfin/alert_manager/alert_processor.py	67.74% <100.00%> (ø)
delfin/common/constants.py	100.00% <100.00%> (ø)
delfin/task_manager/tasks/alerts.py	92.68% <100.00%> (ø)
delfin/drivers/fake_storage/__init__.py	95.17% <0.00%> (+0.76%)	⬆️
... and 1 more

[wisererik]

LGTM

[joseph-v]

LGTM