fix: EMFILE error on macOS Catalina

[kumakichi]

go version go1.14.6 darwin/amd64

gops/goprocess/gp.go

Line 106 in 983b7ba

versionInfo, err = goversion.ReadExe(path)

goversion.ReadExe will return EMFILE error because of no concurrency goroutines limit in:

gops/goprocess/gp.go

Line 29 in 983b7ba

func FindAll() []P {

this error will make some Go processes unrecognized, this PR just add a concurrency limit to solve this problem

[tklauser]

FWIW, I cannot reproduce this issue on macOS Catalina 10.15.6 (i.e. I never get EMFILE). How could I reproduce this to verify this PR fixes the issue?

Would also be nice to add a test for it if this is easily reproducible.

[kumakichi]

Hi, tklauser. I add a test to show the original error i got on my mac(Catalina ,10.15.5)

And I tested on my colleague's computer mac, got the same problem，and his system is also 10.15.5

[tklauser]

Thanks for the update and the explanation @kumakichi. Given that the test is dependent on the number of processes on the system the test runs on, it's probably not very reliable and would lead to flaky tests. So I'd rather drop TestEMFILE again. Sorry for the back and forth.

The rest of the change LGTM now, thanks!