[installer]: Prevent filesystem corruption (#7264)

This improvement reads current SONiC version directly from `/proc/cmdline`.
it supports `grub/aboot/uboot` bootloaders.

**Code snippet**:
```bash
cat /proc/cmdline | sed -n 's/^.*loop=\/*image-\(\S\+\)\/.*$/\1/p'
```

**Description**:
```
-n         don't print lines
s          substitute
^.*        matches anything before the <image_version>
loop=      matches <loop> kernel parameter
\/*image-  matches <image_version> prefix
\(\S\+\)   matches <image_version> group and assigns it to \1
\/.*$      matches anything after the <image_version>
\1         replace everything with <image_version>
p          print it
```
closes #6267

#### Why I did it
* To fix #6267

#### How I did it
* Fixed installer scripts

#### How to verify it
1. Write invalid SONiC version to sonic_version.yml
2. Run SONiC-To-SONiC update

installer/arm64/install.sh

@@ -98,7 +98,13 @@ if [ "$install_env" = "onie" ]; then
     mount_partition
 elif [ "$install_env" = "sonic" ]; then
     demo_mnt="/host"
-    eval running_sonic_revision=$(cat /etc/sonic/sonic_version.yml | grep build_version | cut -f2 -d" ")
+    # Get current SONiC image (grub/aboot/uboot)
+    eval running_sonic_revision="$(cat /proc/cmdline | sed -n 's/^.*loop=\/*image-\(\S\+\)\/.*$/\1/p')"
+    # Verify SONiC image exists
+    if [ ! -d "$demo_mnt/image-$running_sonic_revision" ]; then
+        echo "ERROR: SONiC installation is corrupted: path $demo_mnt/image-$running_sonic_revision doesn't exist"
+        exit 1
+    fi
     # Prevent installing existing SONiC if it is running
     if [ "$image_dir" = "image-$running_sonic_revision" ]; then
         echo "Not installing SONiC version $running_sonic_revision, as current running SONiC has the same version"

installer/armhf/install.sh

@@ -98,7 +98,13 @@ if [ "$install_env" = "onie" ]; then
     mount_partition
 elif [ "$install_env" = "sonic" ]; then
     demo_mnt="/host"
-    eval running_sonic_revision=$(cat /etc/sonic/sonic_version.yml | grep build_version | cut -f2 -d" ")
+    # Get current SONiC image (grub/aboot/uboot)
+    eval running_sonic_revision="$(cat /proc/cmdline | sed -n 's/^.*loop=\/*image-\(\S\+\)\/.*$/\1/p')"
+    # Verify SONiC image exists
+    if [ ! -d "$demo_mnt/image-$running_sonic_revision" ]; then
+        echo "ERROR: SONiC installation is corrupted: path $demo_mnt/image-$running_sonic_revision doesn't exist"
+        exit 1
+    fi
     # Prevent installing existing SONiC if it is running
     if [ "$image_dir" = "image-$running_sonic_revision" ]; then
         echo "Not installing SONiC version $running_sonic_revision, as current running SONiC has the same version"

installer/x86_64/install.sh

@@ -447,7 +447,13 @@ if [ "$install_env" = "onie" ]; then
 
 elif [ "$install_env" = "sonic" ]; then
     demo_mnt="/host"
-    eval running_sonic_revision=$(cat /etc/sonic/sonic_version.yml | grep build_version | cut -f2 -d" ")
+    # Get current SONiC image (grub/aboot/uboot)
+    eval running_sonic_revision="$(cat /proc/cmdline | sed -n 's/^.*loop=\/*image-\(\S\+\)\/.*$/\1/p')"
+    # Verify SONiC image exists
+    if [ ! -d "$demo_mnt/image-$running_sonic_revision" ]; then
+        echo "ERROR: SONiC installation is corrupted: path $demo_mnt/image-$running_sonic_revision doesn't exist"
+        exit 1
+    fi
     # Prevent installing existing SONiC if it is running
     if [ "$image_dir" = "image-$running_sonic_revision" ]; then
         echo "Not installing SONiC version $running_sonic_revision, as current running SONiC has the same version"