netplan-dbus now waits for the spawned 'netplan try' child to touch the /run/netplan/netplan-try.ready stamp file before it returns the DBus call. If no stamp file is detected within up to 5 sec it hits a timeout and returns an error.

Additionally, this PR places ephemeral netplan configs in /run/netplan/config-XXXXXX, to avoid potential exploits of tmpfiles, like https://lwn.net/Articles/250468/

COMMITS:
* test:dbus: some cleanup
* test:utils: add touch() method to MockCmd
* cli:try: add touch/clear_ready_stamp methods
* dbus: wait for 'netplan try' to be ready
netplan-dbus now waits for the spawned 'netplan try' child to touch the
/tmp/netplan-try.ready stamp file before it returns the DBus call. If no
stamp file is detected within up to 5sec it hits a timeout and returns an
error.
* cli:apply: some more time for NM to have all interfaces created
* dbus:cli: move netplan-try.ready stamp file to /run/netplan
to avoid potential expolits of tmpfiles, like https://lwn.net/Articles/250468/
* dbus: move ephemeral netplan config states to /run/netplan
to avoid potential expolits of tmpfiles, like https://lwn.net/Articles/250468/