LlapDecider takes care of tagging certain vertices in the execution graph as
"llap", which in turn causes them to be submitted to an llap daemon instead
of a regular yarn container.
The actual algorithm used is driven by LLAP_EXECUTION_MODE. "all", "none" and
"map" mechanically tag those elements. "auto" tries to be smarter by looking
for suitable vertices.
Regardless of the algorithm used, it's always ensured that there's not user
code that will be sent to the daemon (ie.: script operators, temporary