It appears folks are using the taskflow.utils code in there own
code-bases (likely taking it from the examples) which we do not
want to encourage, so remove the usage of **most** of
taskflow.utils code from the examples so that people are less
likely to copy/paste/reference it.

Change-Id: I0ce3c520de347e3e746e7912aa1366a515458424

To make it possible to alter the runtime flow via a simple
conditional like structure make it possible to have the graph
flow link function take a decider that is expected to be some
callable that will decide (via a boolean return) whether the
edge should actually be traversed when running. When a decider
returns false; the affected + successors will be set into the
IGNORE state and they will be exempt from future runtime and
scheduling decisions.

Part of blueprint taskflow-conditional-execution

Change-Id: Iab0ee46f86d6b8e747911174d54a7295b3fa404d