Fix fast-reboot handling for swss script

[vaibhavhd]

- Why I did it
Modified fast/warm reboot handling for swss script.

- How I did it
Changes added:
For Fast and warm reboot, do not stop peer and dependent services.
Do not perform service stop for fast/warm reboot.
Clear FAST_REBOOT flag only when it is NOT fast reboot mode.

- How to verify it
With and without this change, the fast-reboot and warm-reboot procedure continue as usual. So there is no immediate disruption to the existing procedure.

- Which release branch to backport (provide reason below if seleted)

• 201811
• 201911
• 202006

- Description for the changelog

- Warm disabled
sudo systemctl stop swss

Jul 29 19:16:54.206439 str-s6100-acs-4 NOTICE root: Stopping swss service...
Jul 29 19:16:54.214536 str-s6100-acs-4 NOTICE root: Locking /tmp/swss-syncd-lock from swss service
Jul 29 19:16:54.226242 str-s6100-acs-4 NOTICE root: Locked /tmp/swss-syncd-lock (10) from swss service
Jul 29 19:16:54.682275 str-s6100-acs-4 NOTICE root: Warm boot flag: swss false.
Jul 29 19:16:54.909508 str-s6100-acs-4 NOTICE root: Fast boot flag: swss false.
Jul 29 19:16:58.202710 str-s6100-acs-4 INFO containerd[1187]: time="2020-07-29T19:16:58.202515714Z" level=info msg="shim reaped" id=6d4e9eaab90f34f37fe2830156f8b5707bbdbdaff6f480dd1658cee7b8109023
Jul 29 19:16:58.214503 str-s6100-acs-4 INFO dockerd[1188]: time="2020-07-29T19:16:58.213577510Z" level=info msg="ignoring event" module=libcontainerd namespace=moby topic=/tasks/delete type="*events.TaskDelete"
Jul 29 19:16:58.618211 str-s6100-acs-4 INFO swss.sh[3191]: 0
Jul 29 19:16:58.618893 str-s6100-acs-4 INFO swss.sh[7529]: swss
Jul 29 19:16:58.628091 str-s6100-acs-4 NOTICE root: Stopped swss service...

sudo systemctl start swss

Jul 29 19:25:04.566701 str-s6100-acs-4 NOTICE root: Starting swss service...
Jul 29 19:25:04.575282 str-s6100-acs-4 NOTICE root: Locking /tmp/swss-syncd-lock from swss service
Jul 29 19:25:04.585707 str-s6100-acs-4 NOTICE root: Locked /tmp/swss-syncd-lock (10) from swss service
Jul 29 19:25:05.489071 str-s6100-acs-4 NOTICE root: Warm boot flag: swss false.
Jul 29 19:25:05.496695 str-s6100-acs-4 NOTICE root: Flushing APP, ASIC, COUNTER, CONFIG, and partial STATE databases ...
Jul 29 19:25:05.689886 str-s6100-acs-4 INFO swss.sh[10035]: OK
Jul 29 19:25:06.619944 str-s6100-acs-4 INFO bgp#bgpcfgd: Delete command is not supported for set src templates
Jul 29 19:25:06.389959 str-s6100-acs-4 INFO swss.sh[10035]: message repeated 3 times: [ OK]
Jul 29 19:25:08.349384 str-s6100-acs-4 INFO swss.sh[10035]: Starting existing swss container with HWSKU Force10-S6100
Jul 29 19:25:08.621046 str-s6100-acs-4 INFO containerd[1187]: time="2020-07-29T19:25:08.620750843Z" level=info msg="shim containerd-shim started" address="/containerd-shim/moby/6d4e9eaab90f34f37fe2830156f8b5707bbdbdaff6f480dd1658cee7b8109023/shim.sock" debug=false pid=10365
Jul 29 19:25:08.791312 str-s6100-acs-4 INFO swss.sh[10035]: swss
Jul 29 19:25:09.232504 str-s6100-acs-4 NOTICE root: Started swss service...

- Warm enabled

sudo systemctl stop swss

Jul 29 19:30:51.797353 str-s6100-acs-4 NOTICE root: Stopping swss service...
Jul 29 19:30:51.804830 str-s6100-acs-4 NOTICE root: Locking /tmp/swss-syncd-lock from swss service
Jul 29 19:30:51.814063 str-s6100-acs-4 NOTICE root: Locked /tmp/swss-syncd-lock (10) from swss service
Jul 29 19:30:52.286197 str-s6100-acs-4 NOTICE root: Warm boot flag: swss true.
Jul 29 19:30:52.525833 str-s6100-acs-4 NOTICE root: Fast boot flag: swss false.
Jul 29 19:30:52.533910 str-s6100-acs-4 NOTICE root: Clearing FAST_REBOOT flag...
Jul 29 19:30:52.769908 str-s6100-acs-4 NOTICE root: Unlocking /tmp/swss-syncd-lock (10) from swss service
Jul 29 19:30:52.787214 str-s6100-acs-4 INFO systemd[1]: Stopped switch state service.

sudo systemctl start swss

Jul 29 19:31:13.709335 str-s6100-acs-4 INFO systemd[1]: Starting switch state service...
Jul 29 19:31:13.719837 str-s6100-acs-4 NOTICE root: Starting swss service...
Jul 29 19:31:13.727581 str-s6100-acs-4 NOTICE root: Locking /tmp/swss-syncd-lock from swss service
Jul 29 19:31:13.736647 str-s6100-acs-4 NOTICE root: Locked /tmp/swss-syncd-lock (10) from swss service
Jul 29 19:31:14.869476 str-s6100-acs-4 NOTICE root: Warm boot flag: swss true.
Jul 29 19:31:16.578414 str-s6100-acs-4 INFO swss.sh[15481]: Starting existing swss container with HWSKU Force10-S6100
Jul 29 19:31:16.653156 str-s6100-acs-4 INFO swss.sh[15481]: swss
Jul 29 19:31:17.127692 str-s6100-acs-4 NOTICE root: Started swss service...

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