Create path to local sockets if it doesn't exist

[brendonj]

The client tries to create a few files (unix domain sockets etc) in the AMP_RUN_DIR which is only created by the init script. If you don't use the init script then the directory doesn't get created and the client fails to create the files:

DEBUG: Creating local socket at '/var/run/amplet2/localhost.sock'
WARNING: Failed to bind local socket: No such file or directory
ALERT: Failed to initialise local resolver, aborting

The client should probably ensure that the directory exists before trying to create files inside it. Is it better to create the AMP_RUN_DIR once at startup, or check the path exists in initialise_local_socket() each time in case it is called with unusual directories at some point in the future?