Add an option to avoid creating a tmpfs in prepare()

Root access is required for creating tmpfs mounts in the context of
the current mount namespace, and creating a tmpfs in the context of a
new mount namespace is less useful because a process in the parent
namespace can't easily access it.

So add an option to avoid creating tmpfs mounts, which will be used by
the rootless bootstrap mode for now.

In addition, when tmp directories aren't mounted as tmpfs, their
contents can't be removed using os.umount(). So instead remove them
recursively using shutil.rmtree().

sysc.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 """System C"""
 # SPDX-License-Identifier: GPL-3.0-or-later
+# SPDX-FileCopyrightText: 2022 Dor Askayo <dor.askayo@gmail.com>
 # SPDX-FileCopyrightText: 2021-22 fosslinux <fosslinux@aussies.space>
 # SPDX-FileCopyrightText: 2021 Andrius Štikonas <andrius@stikonas.eu>
 
@@ -31,7 +32,6 @@ class SysC(SysGeneral):
             self.tmp_dir = os.path.join(self.sys_dir, 'tmp')
         else:
             self.tmp_dir = os.path.join(tmpdir, 'sysc')
-            os.mkdir(self.tmp_dir)
 
     def __del__(self):
         if not self.preserve_tmp:
@@ -41,11 +41,14 @@ class SysC(SysGeneral):
 
         super().__del__()
 
-    def prepare(self, create_disk_image):
+    def prepare(self, mount_tmpfs, create_disk_image):
         """
         Prepare directory structure for System C.
         """
-        self.mount_tmpfs()
+        if mount_tmpfs:
+            self.mount_tmpfs()
+        else:
+            os.mkdir(self.tmp_dir)
 
         rootfs_dir = None