Fix sfputil CLI failure for multi-asic platforms

[longhuan-cisco]

What I did

This PR is to fix issue #3167

Basically sfputil Cli became broken on multi-asic platforms after introduction of sonic-net/sonic-buildimage#10960 which removed the initialization of global DB config from portconfig.py (library side) and expects application to do it, but here application side (sfputil) was not updated accordingly.

How I did it

Add load_db_config call to sfputil for initialization

How to verify it

Before fix:

root@sonic:/home# sfputil show presence                                                                                                                                                                                     
Error reading port info (:- validateNamespace: Initialize global DB config using API SonicDBConfig::initializeGlobalConfig)                                                                                                       

After fix:

root@sonic:/home# sfputil show presence
Port         Presence                                   
-----------  -----------                                
Ethernet0    Present                                    
Ethernet4    Not present                                
Ethernet8    Present                                    
Ethernet12   Present                                    
Ethernet16   Not present       
...

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[longhuan-cisco]

@prgeor @abdosi @SuvarnaMeenakshi @bmridul
Please take a look, thanks

[SuvarnaMeenakshi]

lgtm

[prgeor]

@prgeor @abdosi @SuvarnaMeenakshi @bmridul Please take a look, thanks

@longhuan-cisco please test this on NON-multi asic platform

[longhuan-cisco]

@longhuan-cisco please test this on NON-multi asic platform

@prgeor Verified on non-multi-asic platforms also:

root@sonic:/home# ls /run/redis/sonic-db/
database_config.json
root@sonic:/home# sfputil show presence
Port         Presence
-----------  -----------
Ethernet0    Present
Ethernet8    Present
Ethernet16   Present
Ethernet24   Present
Ethernet32   Present
...

[xumia]

/azp run Azure.sonic-utilities

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[qiluo-msft]

/azp run Azure.sonic-utilities

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[prgeor]

@longhuan-cisco please check the code coverage

[longhuan-cisco]

@longhuan-cisco please check the code coverage

@prgeor addressed it.