plugins: add max retry logic for rild connect

This change adds a maximum retry count for connecting to
rild.  After ~30s, rild will give up trying to connect.
This changes the current behavior which will retry forever.

Note that in order for this to work, the an explicity respawn limit needs to be added to the ofono upstart job ( currently an override shipped by lxc-android-config ):

respawn limit 4 150

This means stop ofono if it respawns four times in 2 1/2 m.