Clear /tmp when booting

This matches the behavior of most UNIX systems and ensures that the disk
doesn't eventually fills entirely with unused temporary files.

config/base.toml

@@ -20,6 +20,10 @@ ptyd = {}
 [[files]]
 path = "/etc/init.d/00_base"
 data = """
+# clear and recreate tmpdir with 0o1777 permission
+rm -r /tmp
+mkdir -m a=rwxt /tmp
+
 ipcd
 ptyd
 escalated
@@ -86,13 +90,6 @@ path = "/share"
 data = "usr/share"
 symlink = true
 
-## /tmp directory with special mode
-[[files]]
-path = "/tmp"
-data = ""
-directory = true
-mode = 0o1777
-
 ## Device file symlinks
 [[files]]
 path = "/dev/null"