[jsk_fetch_startup] Add poke to correct_position.py to avoid diagnostics error

[708yamaguchi]

From knorth55#255

Depends on jsk-ros-pkg/jsk_common#1740

In correct_position.py, fetch publishes initialpose topic to amcl node when the following 2 conditions are met.

• initialpose topic is subscribed by amcl
• fetch is docking

I this case, even if initialpose is subscribed, it does not necessarily mean that publish is performed.
So I manually call poke() in callback function in addition to publish().

cc @iory @knorth55