Fix prestage ISO install abort if previous subcloud install exists

This commit fixes the detection of www/pages/feed/rel-xx.x/install_uuid
via device '/dev/cgts-vg/var-lv'. There was a bug which was always
mounting the same device, rather than the proper device_list.

The code is also slightly refactored for simplification and clarity.

Test Plan
PASS:
- Generate ISO using gen-prestage-iso.sh without --force-install option
    - Verify installation failure (drop to boot prompt) if previous
      subcloud installation exists
    - Verify successful subcloud installation if no previous
      subcloud installation exists
- Generate ISO using gen-prestage-iso.sh with --force-install option
    - Verify successful installation regardless if previous subcloud
      installation exists or not

Closes-Bug: 2020526
Change-Id: Ib83d72fa07335ffa29d365da7813b226c4ef310b
Signed-off-by: Kyle MacLeod <kyle.macleod@windriver.com>

kickstart/files/kickstart.cfg

@@ -1103,30 +1103,28 @@ if check_prestage -eq 0 ; then
 
         ilog "Searching for existing installation..."
 
-        device_list=()
+        # Build up device_list to search for existing installation.
+        # We will look for the install_uuid file on each of the devices in the list.
+        # First, if volume groups have been enabled, we can mount /dev/cgts-vg/var-lv
+        device_list=("/dev/cgts-vg/var-lv")
+
+        # Now add the rest of the rootfs partitions to device_list
         for part in "${part_numbers[@]}"; do
-            device=${rootfs_part_prefix}${part}
+            device_list+=("${rootfs_part_prefix}${part}")
-            device_list+=(${device})
-            ilog "Adding ${device}"
         done
 
-        # adding the following device to the device list to search
+        ilog "Checking device_list: ${device_list[*]}"
-        # for the filesystem. If Volume Groups have been enabled,
+        for device in "${device_list[@]}"; do
-        # it is possible to perform the checks for install_guid below
-        # by mounting /dev/cgts-vg/var-lv.
-        device_list+=("/dev/cgts-vg/var-lv")
-        ilog "Adding /dev/cgts-vg/var-lv"
-
-        for part in "${device_list[@]}"; do
             # mount this part at a temporary mount point
-            mount ${device} ${temp_mount}
+            ilog "Checking device: ${device}"
-            if [ $? -ne 0 ]; then
+            mount "${device}" "${temp_mount}"
-                wlog "Unable to mount ${device}"
+            rc=$?
+            if [ "${rc}" -ne 0 ]; then
+                wlog "Unable to mount ${device}, rc=${rc}"
                 continue
             fi
-            # Check for the presence of install_uuid in one of the partitions on
+            # Check for the presence of install_uuid in one of the partitions on the device_list
-            # the root device
+            if [ -e "${temp_mount}/www/pages/feed/rel-xxxPLATFORM_RELEASExxx/install_uuid" ]; then
-            if [[ -e "${temp_mount}/www/pages/feed/rel-xxxPLATFORM_RELEASExxx/install_uuid" ]]; then
                 wlog "Found valid installation on ${device}"
                 umount ${temp_mount}
                 # Do not modify the system in any way