[sonic_installer] Firmware upgrade log is not a part of syslog

[nazariig]

Description

SONiC journal is missing info related to image firmware upgrade.
This makes an issues with failures analysis when working with techsupport file.

Steps to reproduce the issue:

1. sonic-installer install sonic-mellanox.bin

Describe the results you received:

root@sonic:/home/admin# sonic-installer install sonic-mellanox.bin
New image will be installed, continue? [y/N]: y
Installing image SONiC-OS-201911.263-35fc12c3 and setting it as default...
Command: bash ./sonic-mellanox.bin
/tmp/tmp.gJ7CKnoyWE/installer/install.sh: 547: /tmp/tmp.gJ7CKnoyWE/installer/install.sh: [[: not found
Verifying image checksum ... OK.
Preparing image archive ... OK.
Installing SONiC in SONiC
ONIE Installer: platform: x86_64-mellanox-r0
onie_platform: x86_64-mlnx_msn4700-r0
Installing SONiC to /host/image-201911.263-35fc12c3
Archive:  fs.zip
   creating: /host/image-201911.263-35fc12c3/boot/
  inflating: /host/image-201911.263-35fc12c3/boot/vmlinuz-4.9.0-11-2-amd64
  inflating: /host/image-201911.263-35fc12c3/boot/config-4.9.0-11-2-amd64
  inflating: /host/image-201911.263-35fc12c3/boot/initrd.img-4.9.0-11-2-amd64
  inflating: /host/image-201911.263-35fc12c3/boot/System.map-4.9.0-11-2-amd64
   creating: /host/image-201911.263-35fc12c3/platform/
   creating: /host/image-201911.263-35fc12c3/platform/x86_64-grub/
  inflating: /host/image-201911.263-35fc12c3/platform/x86_64-grub/grub-pc-bin_2.02~beta3-5+deb9u2_amd64.deb
 extracting: /host/image-201911.263-35fc12c3/platform/firsttime
  inflating: /host/image-201911.263-35fc12c3/fs.squashfs
Switch CPU vendor is: GenuineIntel
Installed SONiC base image SONiC-OS successfully

Command: grub-set-default --boot-directory=/host 0

Command: config-setup backup
Taking backup of curent configuration

Command: mkdir -p /tmp/image-201911.263-35fc12c3-fs
Command: mount -t squashfs /host/image-201911.263-35fc12c3/fs.squashfs /tmp/image-201911.263-35fc12c3-fs
Command: sonic-cfggen -d -y /tmp/image-201911.263-35fc12c3-fs/etc/sonic/sonic_version.yml -t /tmp/image-201911.263-35fc12c3-fs/usr/share/sonic/templates/sonic-environment.j2
Command: umount -rf /tmp/image-201911.263-35fc12c3-fs
Command: rm -rf /tmp/image-201911.263-35fc12c3-fs
Command: sync;sync;sync

Command: sleep 3

Done

root@sonic:/home/admin# tail -F /var/log/syslog

Describe the results you expected:
The stdout/stderr of firmware upgrade log should be also redirected to syslog

Additional information you deem important (e.g. issue happens only occasionally):
Output of show version:

(paste your output here)

Attach debug file sudo generate_dump:

(paste your output here)