[DISCUSS] FLIP-138: Declarative Resource management

[Chesnay Schepler]

Hello,

in FLIP-138 we want to rework the way the JobMaster acquires slots, such 
that required resources are declared before a job is scheduled and th 
job execution is adjusted according to the provided resources (e.g., 
reducing parallelism), instead of asking for a fixed number of resources 
during scheduling and failing midway through if not enough resources are 
available.

This is a stepping stone towards reactive mode, where Flink will 
automatically make use of new TaskExecutors being started.

More details can be found here 
<https://cwiki.apache.org/confluence/display/FLINK/FLIP-138%3A+Declarative+Resource+management>.