[arista]: Fix convertfs condition for booting from EOS (sonic-net#4139)

Fix the issue of incorrectly skipping the convertfs hook when fast-reboot from EOS, by adding an extra kernel cmdline param "prev_os" to differentiate fast-reboot from EOS and from SONiC.

This is because we still do disk conversion for fast reboot from eos to sonic, like format the disk.

files/Aboot/boot0.j2

@@ -362,7 +362,7 @@ write_boot_configs() {
 }
 
 run_kexec() {
-    local cmdline="$(cat $cmdline_image | tr '\n' ' ')"
+    local cmdline="$(cat $cmdline_image | tr '\n' ' ') $ENV_EXTRA_CMDLINE"
     local kernel="${KERNEL:-$(find $image_path/boot -name 'vmlinuz-*' -type f | head -n 1)}"
     local initrd="${INITRD:-$(find $image_path/boot -name 'initrd.img-*' -type f | head -n 1)}"
 

files/initramfs-tools/arista-convertfs.j2

@@ -18,6 +18,8 @@ flash_dev=''
 block_flash=''
 aboot_flag=''
 backup_file=''
+prev_os=''
+sonic_fast_reboot=''
 
 # Wait until get the fullpath of flash device, e.g., /dev/sda
 wait_get_flash_dev() {
@@ -133,16 +135,21 @@ for x in "$@"; do
         docker_inram=*)
             docker_inram="${x#docker_inram=}"
             ;;
+        prev_os=*)
+            prev_os="${x#prev_os=}"
+            ;;
         SONIC_BOOT_TYPE=warm*|SONIC_BOOT_TYPE=fast*)
-            # Skip this script for warm-reboot and fast-reboot
-            exit 0
+            sonic_fast_reboot=true
             ;;
     esac
 done
 
 # Check aboot
 [ -z "$aboot_flag" ] && exit 0
 
+# Skip this script for warm-reboot/fast-reboot from sonic
+[ "$sonic_fast_reboot" == true ] && [ "$prev_os" != eos ] && exit 0
+
 # Get flash dev name
 if [ -z "$block_flash" ]; then
     echo "Error: flash device info is not provided"