Only set image backup to complete if sync file could be created
Only set image backup to complete if sync file could be created

(cherry picked from commit 3263a5d60927419f3adbffa86958e5021f5f0579)

# Conflicts:
#	urbackupserver/ImageBackup.cpp

uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend