Added utility functions for ensurance of pose transformation

These functions were formerly part of cram_moveit, but turned out to be non-moveit-specific. As they are used in other packages, they are moved to cl-tf2 to not introduce unnecessary dependencies towards cram_bridge (which contains cram_moveit).
Ah, right. This is `with-failure-handling`, isn't it?
I'll see after replacing it with a lower-level handler-case, so that the `tf2-server-error` in https://github.com/ros/roslisp_common/blob/master/cl_tf2/src/buffer-client.lisp#L48 is captured.