[action] [PR:17342] [config-chassisdb] use cached variables

[mssonicbld]

No cache:

root@arc-switch1004:/home/admin# time bash -x /usr/bin/config-chassisdb
+ config_chassis_db
+ startdb_file=/etc/sonic/chassisdb.conf
+ '[' '!' -e /etc/sonic/chassisdb.conf ']'
++ sonic-cfggen -H -v DEVICE_METADATA.localhost.platform
+ platform=x86_64-mlnx_msn2700-r0
+ chassis_config=/usr/share/sonic/device/x86_64-mlnx_msn2700-r0/chassisdb.conf
+ '[' '!' -e /usr/share/sonic/device/x86_64-mlnx_msn2700-r0/chassisdb.conf ']'
+ echo 'no chassisdb.conf found, bypass config-chassisdb service'
no chassisdb.conf found, bypass config-chassisdb service
+ exit 0

real 0m0.512s
user 0m0.429s
sys 0m0.058s

With cache:

root@arc-switch1004:/home/admin# time bash -x /usr/bin/config-chassisdb
+ '[' -f /etc/sonic/sonic-environment ']'
+ . /etc/sonic/sonic-environment
++ SONIC_VERSION=202305_RC.32-da745b71d_Internal
++ PLATFORM=x86_64-mlnx_msn2700-r0
++ HWSKU=Mellanox-SN2700-D48C8
++ DEVICE_TYPE=ToRRouter
++ ASIC_TYPE=mellanox
+ config_chassis_db
+ startdb_file=/etc/sonic/chassisdb.conf
+ '[' '!' -e /etc/sonic/chassisdb.conf ']'
+ platform=x86_64-mlnx_msn2700-r0
+ chassis_config=/usr/share/sonic/device/x86_64-mlnx_msn2700-r0/chassisdb.conf
+ '[' '!' -e /usr/share/sonic/device/x86_64-mlnx_msn2700-r0/chassisdb.conf ']'
+ echo 'no chassisdb.conf found, bypass config-chassisdb service'
no chassisdb.conf found, bypass config-chassisdb service
+ exit 0

real 0m0.017s
user 0m0.005s
sys 0m0.008s

Why I did it

Improve boot performance mostly needed for fast and warmboot

Work item tracking

• Microsoft ADO (number only):

How I did it

Use cached variable.

How to verify it

Boot the system. Simply do "systemd-analyze blame" and look at service start time.

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211
• 202305
• 202311

Tested branch (Please provide the tested image version)

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[mssonicbld]

Original PR: #17342