bugfix: set random seed for each worker process at init_worker phase, only init phase is not enough.

[membphis]

What this PR does / why we need it:

related PR: #2306

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible?

[membphis]

@zlm0125 welcome to review and make a test with this PR. I think it should work fine for your case

[moonming]

why only init phase is not enough?

[membphis]

why only init phase is not enough?

init works in master process if the lua_code_cache is on.

We want to set different seed for different work processes, so we should use init_worker phase.

we can delete those code https://github.com/apache/apisix/pull/2357/files#diff-d982d52466e7c93c7b604358339b2a29R85-R90 .
And run the test case, then we will get the same random number which is wrong.

Here is the right one:

[moonming]

related PR: #2306

I don't understand what it has to do with this PR.
#2306 did not show any details.

[moonming]

And we should remove random in init phase if add random in init_worker phase.

[membphis]

And we should remove random in init phase if add random in init_worker phase.

you are right. let me do this later.