Fix LVM snapshot and disk space logic (closes #1986) (#2779)

* Fix LVM snapshot and disk space logic (closes #1986)

- Ask about snapshots first before disk space question
- Reserve 10G for snapshots, then extend with remaining free space
- This prevents the bug where extending to 100%FREE consumed space needed for snapshots
- Provisioning mode still always extends as before
- Fix whiptail installation to run apt-get update first

* Export and unset SNAPSHOTS_ENABLED and USE_ALL_DISK_SPACE variables

- Export variables when set to make them available to child processes
- Unset them after use to clean up the environment
- Fixes shellcheck SC2034 warning

Author: enoch85

nextcloud_install_production.sh

@@ -31,6 +31,7 @@ if dpkg-query -W -f='${Status}' "whiptail" 2>/dev/null | grep -q "ok installed"
 then
     echo "whiptail OK"
 else
+    apt-get update -q4
     apt-get install whiptail -y
 fi
 
@@ -99,6 +100,8 @@ then
 fi
 
 # Create a placeholder volume before modifying anything
+# Ask about snapshots first
+export SNAPSHOTS_ENABLED=""
 if [ -z "$PROVISIONING" ]
 then
     if ! does_snapshot_exist "NcVM-installation" && yesno_box_no "Do you want to use LVM snapshots to be able to restore your root partition during upgrades and such?
@@ -113,7 +116,8 @@ Enabling this will also force an automatic reboot after running the update scrip
             print_text_in_color "$ICyan" "Creating volume..."
             sleep 1
             # Create a placeholder snapshot
-            check_command lvcreate --size 5G --name "NcVM-installation" ubuntu-vg
+            check_command lvcreate --size 10G --name "NcVM-installation" ubuntu-vg
+            export SNAPSHOTS_ENABLED="yes"
         else
             print_text_in_color "$IRed" "Could not create volume because of insufficient space..."
             sleep 2
@@ -122,10 +126,21 @@ Enabling this will also force an automatic reboot after running the update scrip
 fi
 
 # Fix LVM on BASE image
+# Ask about disk space - now snapshots have been reserved, we can use remaining space
+export USE_ALL_DISK_SPACE=""
 if grep -q "LVM" /etc/fstab
 then
+    # In provisioning mode, always extend
+    # In normal mode, ask the user
     if [ -n "$PROVISIONING" ] || yesno_box_yes "Do you want to make all free space available to your root partition?"
     then
+        export USE_ALL_DISK_SPACE="yes"
+    fi
+fi
+
+# Extend LVM if requested
+if [ "$USE_ALL_DISK_SPACE" = "yes" ]
+then
     # Resize LVM (live installer is &%¤%/!
     # VM
     print_text_in_color "$ICyan" "Extending LVM, this may take a long time..."
@@ -150,9 +165,12 @@ then
             fi
         fi
     done
-    fi
 fi
 
+# Cleanup environment variables
+unset SNAPSHOTS_ENABLED
+unset USE_ALL_DISK_SPACE
+
 # Install needed dependencies
 install_if_not lshw
 install_if_not net-tools