nocloud: create temp mount dir under /run

The /run is usually a tmpfs which is automatically removed on reboot.
Use this for the temp mount dir so we don't leave any /mnt/cidata-* temp
leftovers.

Also explicitly create the parent directory of the temp dir, which may
no exist.  This solved a weird case where running tests locally ended up
hanging in mount.

lib/tiny-cloud/cloud/nocloud/imds

@@ -47,7 +47,8 @@ _load_nocloud_cmdline() {
 }
 
 _load_nocloud_volume() {
-    local mntdir=$(mktemp -d "$ROOT/mnt/cidata-XXXXXX")
+    mkdir -p "$ROOT"/run/tiny-cloud
+    local mntdir=$(mktemp -d "$ROOT/run/tiny-cloud/cidata-XXXXXX")
     local data mounted
 
     mkdir -p "$mntdir"