Backport vmtools version in vmdk (LP: #1893898)

Backport
LP: #1893898 describes missing vmtools version from the vmdk headers.
The version should be added as ddb.toolsVersion = "2147483647" however
the sed was no longer replacing a ddb.comment field with the tools
version. Rather than subbing ddb.comment with toolsVersion, this commit
deletes ddb.comment (which the comment mentions could cause errors),
and adds the correct value. There was no visibility into the descriptor
during hook creation, so debug statements were added. This allows us to
quickly verify in the logs that bad statements are removed (the possibly
offending comments), as well as ensuring that the toolsVersion is added

live-build/functions

@@ -206,28 +206,33 @@ modify_vmdk_header() {
 
     # Extract the vmdk header for manipulation
     dd if="${vmdk_name}" of="${descriptor}" bs=1 skip=512 count=1024
+    echo "Cat'ing original vmdk disk descriptor to console for debugging."
+    # cat header so we are aware of the original descriptor for debugging
+    cat $descriptor
 
-    # The sed lines below is where the magic is. Specifically:
-    #   ddb.toolsVersion: sets the open-vm-tools so that VMware shows
-    #       the tooling as current
-    #   ddb.virtualHWVersion: set the version to 7, which covers most
-    #       current versions of VMware
-    #   createType: make sure its set to stream Optimized
-    #   remove the vmdk-stream-converter comment and replace with
-    #       # Disk DescriptorFile. This is needed for Virtualbox
-    #   remove the comments from vmdk-stream-converter which causes
-    #       VirtualBox and others to fail VMDK validation
-
-    sed -e 's|# Description file.*|# Disk DescriptorFile|' \
-        -e '/# Believe this is random*/d' \
-        -e '/# Indicates no parent/d' \
-        -e '/# The Disk Data Base/d' \
-        -e 's|ddb.comment.*|ddb.toolsVersion = "2147483647"|' \
-            "${descriptor}" > "${newdescriptor}"
-
-    # The header is cannot be bigger than 1024
-    expr $(stat --format=%s ${newdescriptor}) \< 1024 > /dev/null 2>&1 || {
-        echo "descriptor is too large, VMDK will be invalid!"; exit 1; }
+    # trim null bytes to treat as standard text file
+    tr -d '\000' < $descriptor > $newdescriptor
+
+    # add newline to newdescriptor
+    echo "" >> $newdescriptor
+
+    # add required tools version
+    echo -n 'ddb.toolsVersion = "2147483647"' >> $newdescriptor
+
+    # diff original descriptor and new descriptor for debugging
+    # diff exits 1 if difference. pipefail not set so piping diff
+    # to cat prints diff and swallows exit 1
+    echo "Printing diff of original and new descriptors."
+    diff --text $descriptor $newdescriptor | cat
+
+    # The header must be 1024 or less before padding
+    if ! expr $(stat --format=%s ${newdescriptor}) \< 1025 > /dev/null 2>&1; then
+        echo "descriptor is too large, VMDK will be invalid!"; 
+        exit 1
+    fi
+
+    # reset newdescriptor to be 1024
+    truncate --no-create --size=1K $newdescriptor
 
     # Overwrite the vmdk header with our new, modified one
     dd conv=notrunc,nocreat \