[BEAM-2724] Preparing support for Structured Names in Dataflow counters

[pabloem]

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• Adding a CounterName class to help support structured names for counters in the future.
• Also remove function calls from the apiclient.py file that are no longer used.
• And also removing function calls used for aggregators, which have been dead code for a while.

[coveralls]

Changes Unknown when pulling b1e15ab on pabloem:add-countername into ** on apache:master**.

[coveralls]

Coverage remained the same at 69.971% when pulling a4176f8 on pabloem:add-countername into 2fa4fde on apache:master.

[coveralls]

Coverage increased (+0.003%) to 69.975% when pulling a4176f8 on pabloem:add-countername into 2fa4fde on apache:master.

[pabloem]

r: @aaltay
First change to add structured counter names in Dataflow runner. Adding the CounterName class.

[aaltay]

Do you need the hash function? What is the default one?

[pabloem]

The default hash function is related to the id() of the object. This means that without overriding it, this would be True:
hash(CounterName('arg1', 'arg2', 'arg3', 'arg4')) != hash(CounterName('arg1', 'arg2', 'arg3', 'arg4'))

I need counters to be indexable by their name. e.g.

my_d = {CounterName('arg1', 'arg2', 'arg3', 'arg4'): my_counter}
assert my_d[CounterName('arg1', 'arg2', 'arg3', 'arg4')] == my_counter

That's why I need to override the hash function. In fact, I'll add unit tests for this.

[pabloem]

https://stackoverflow.com/questions/11324271/what-is-the-default-hash-in-python

[aaltay]

Thanks

[aaltay]

LGTM