Add units to argument names in ray.init and ray.wait.

[robertnishihara]

This makes the following changes:

• object_store_memory -> object_store_memory_bytes
• redis_max_memory -> redis_max_memory_bytes
• timeout -> timeout_milliseconds

[robertnishihara]

There was some disagreement about whether we should do this or not, so we should discuss this. cc @atumanov @ericl @pcmoritz

@pcmoritz pointed out that it's more common to use timeout in Python and for it to refer to seconds. However, that forces uses to look at the documentation to figure out how to use ray.wait, whereas timeout_milliseconds is much clearer. I'd also be ok with switching to timeout_seconds.

[ericl]

This is a breaking change right? I think we can also switch to mb and s as they are more natural units, i.e. redis_max_memory_mb=5000 is much more readable. Or even gb.

[ericl]

Let's make sure this is merged after #3558 since they will hugely conflict.

[AmplabJenkins]

Test FAILed.
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https://amplab.cs.berkeley.edu/jenkins//job/Ray-PRB/10369/
Test FAILed.

[atumanov]

Yes, I would very much like units to be part of all argument names to make it explicit. Regarding the exact unit abbreviations, there's a standard for this: SI units (le Système International):
https://en.wikipedia.org/wiki/International_System_of_Units
I think we should make our unit abbreviations compatible with the "unit symbols" chosen for SI units. For example, s (seconds), ms (milliseconds). They standardize power of 10 prefixes as well:
https://en.wikipedia.org/wiki/International_System_of_Units#Prefixes
Regarding the comment about following the Python convention -- I think an international standard should supersede any de facto convention. We can lead that convention by example :-)

[robertnishihara]

Replacing with #3666.