Build the rsync command as an argument list

The rsync command was built as a string and split with shlex.split,
so paths containing quotes broke it, and the key file path in the -e
command was split on spaces. Pass each path as its own argument, and
quote the key file and user name inside the -e command, which rsync
splits itself.

simple_backup/simple_backup.py

@@ -552,24 +552,27 @@ class Backup:
 
         logger.info('Copying files. This may take a long time...')
 
-        if self._last_backup == '':
+        # Build the argument list directly, so paths with spaces or quotes are passed unchanged
-            rsync = f'/usr/bin/rsync {self.options} --exclude-from={self._exclude_path} ' +\
+        args = ['/usr/bin/rsync', *self.options.split()]
-                f'--files-from={self._inputs_path} / "{self._server}{self._output_dir}"'
-        else:
-            rsync = f'/usr/bin/rsync {self.options} --link-dest="{self._last_backup}" --exclude-from=' +\
-                f'{self._exclude_path} --files-from={self._inputs_path} / "{self._server}{self._output_dir}"'
 
+        if self._last_backup != '':
+            args.append(f'--link-dest={self._last_backup}')
+
+        args.extend([f'--exclude-from={self._exclude_path}', f'--files-from={self._inputs_path}',
+                     '/', f'{self._server}{self._output_dir}'])
+
+        # rsync splits the -e command itself, so quote the parts that may contain spaces
         if self.ssh_keyfile is not None:
-            rsync = f'{rsync} -e \'ssh -i {self.ssh_keyfile} -o StrictHostKeyChecking=accept-new\''
+            ssh = f'ssh -i {shlex.quote(self.ssh_keyfile)} -o StrictHostKeyChecking=accept-new'
         elif self._password_auth and which('sshpass'):
-            rsync = f'{rsync} -e \'sshpass -e ssh -l {self.ssh_user} -o StrictHostKeyChecking=accept-new\''
+            ssh = f'sshpass -e ssh -l {shlex.quote(self.ssh_user)} -o StrictHostKeyChecking=accept-new'
         else:
-            rsync = f'{rsync} -e \'ssh -o StrictHostKeyChecking=accept-new\''
+            ssh = 'ssh -o StrictHostKeyChecking=accept-new'
+
+        args.extend(['-e', ssh])
 
         if self._remote and self.remote_sudo:
-            rsync = f'{rsync} --rsync-path="sudo rsync"'
+            args.append('--rsync-path=sudo rsync')
-
-        args = shlex.split(rsync)
 
         with Popen(args, stdin=PIPE, stdout=PIPE, stderr=STDOUT, shell=False) as p:
             output: Union[bytes, List[str]]