bmc: sync-once: handle deleted source files

Ensure destination files are removed if the source files are deleted.

Two changes are made to the sync-once script:
1. If the sync entry is not present in the source, remove it from the
destination.
2. Add --delete option to rsync to remove destination files that are not
present in the source.

Tested For first change:
1. For directories that not present in the source, the destination
directory is present.
```
~# tree /etc/systemd/network/
/etc/systemd/network/  [error opening dir]

~# tree /run/media/rwfs-alt/cow/etc/systemd/network/
/run/media/rwfs-alt/cow/etc/systemd/network/
|-- a
|-- b
`-- c
```

2. After running the sync-once script, the destination directory is
removed.
```
~# bash bmc/sync-once.sh
rsync -a -R --delete /etc/hostname /run/media/rwfs-alt/cow
rsync -a -R --delete /etc/machine-id /run/media/rwfs-alt/cow
Removing /run/media/rwfs-alt/cow//etc/systemd/network/

~# tree /run/media/rwfs-alt/cow/etc/systemd/network/
/run/media/rwfs-alt/cow/etc/systemd/network/  [error opening dir]
```

3. For files that are not present in the source, the destination file is
present.
```
~# ls -l /etc/machine-id
ls: cannot access '/etc/machine-id': No such file or directory
~# ls -l /run/media/rwfs-alt/cow/etc/machine-id
-rw-r--r-- 1 root root 33 Feb 14 03:57 /run/media/rwfs-alt/cow/etc/machine-id
```

4. After running the sync-once script, the destination file is removed.
```
~# bash bmc/sync-once.sh
sudo bash bmc/sync-once.sh

~# rsync -a -R --delete /etc/hostname /run/media/rwfs-alt/cow
Removing /run/media/rwfs-alt/cow//etc/machine-id

~# ls -l /run/media/rwfs-alt/cow/etc/machine-id
ls: cannot access '/run/media/rwfs-alt/cow/etc/machine-id': No such file or directory
```

For the second change:
1. if the destination is directory and the destination's files are not
present in the source, the destination files are removed.
```
~# tree /etc/systemd/network/
/etc/systemd/network/
|-- a
`-- c

~# tree /run/media/rwfs-alt/cow/etc/systemd/network/
/run/media/rwfs-alt/cow/etc/systemd/network/
|-- a
|-- b
`-- c

~# bash bmc/sync-once.sh
rsync -a -R --delete /etc/systemd/network/ /run/media/rwfs-alt/cow

~# tree /etc/systemd/network/
/etc/systemd/network/
|-- a
`-- c

~# tree /run/media/rwfs-alt/cow/etc/systemd/network/
/run/media/rwfs-alt/cow/etc/systemd/network/
|-- a
`-- c
```

Change-Id: I81f5adcf1816f1c8d0b153fa2ae4db2860daa43a
Signed-off-by: Jian Zhang <[email protected]>

bmc/sync-once.sh

@@ -8,6 +8,14 @@ SYNCLIST=/etc/synclist
 DEST_DIR=/run/media/rwfs-alt/cow
 
 while read -r l; do
-    echo rsync -a -R "${l}" "${DEST_DIR}"
-    rsync -a -R "${l}" "${DEST_DIR}"
+
+    # if the sync entry is not present in the source, remove it from the destination
+    if [ -n "${l}" ] && [ ! -e "${l}" ] && [ -e "${DEST_DIR}/${l}" ]; then
+        echo "Removing ${DEST_DIR}/${l}"
+        rm -rf "${DEST_DIR:?}/${l:?}"
+        continue
+    fi
+
+    echo rsync -a -R --delete "${l}" "${DEST_DIR}"
+    rsync -a -R --delete "${l}" "${DEST_DIR}"
 done < ${SYNCLIST}