SAMZA-2168: Remove redundant SystemAdmin creation in ApplicationMaster

[shanthoosh]

Samza ApplicationMaster is a process responsible for scheduling, orchestrating and managing the lifecycle of containers of a samza job.

SystemAdmin abstraction is used in samza to validate, create and fetch the metadata of input and metadata streams of the samza job. Creating a SystemAdmin instance for a system is an expensive operation which entails creating the connection with the broker and setting up resources.

Currently, SystemAdmin for a system is created multiple times across the different components of the samza ApplicationMaster. This duplicate SystemAdmin creation happens as a part of the startup sequence of ApplicationMaster and unnecessarily increases the startup time of ApplicationMaster.

[shanthoosh]

@xinyuiscool

Please take a look when you have a chance.

[shanthoosh]

@xinyuiscool

1. I tested this patch with the hello-samza test jobs in open-source.
2. Verified that this patch works fine with samza-yarn and a beam job in LinkedIn.

For the large stateful jobs which consumes a lot of input topics from different systems, I verified that this patch reduces the startup time of ApplicationMaster from 1.5 minutes to 20 seconds.

[mynameborat]

Is this PR still needed?

[shanthoosh]

This patch reduces the number of SystemAdmin instances created in ApplicationMaster startup control flow. This reduces the ApplicationMaster startup time.

Let me fix the merge conflicts and update the patch.

[prateekm]

@shanthoosh FYI, is this PR still relevant?