Set node-predicate in group-spec
Rename node-predicate to node-filter in group-spec
Rename return-value-expr to with-action-values

with-action-values is a clearer name.  return-value-expr remains, but is
deprecated.
Fix channel connection failures on timeout

JSch Session objects seem to timeout and still report that they are connected.
This works around the issue by retrying on a "session is not opened." exception.

Fixes #222