support multiple identical args in SCYLLA_EXT_OPTS

[fruch]

since we have cases multiple --experimental-features needs to be passed via SCYLLA_EXT_OPTS, adding support for key with multiple values in process_opts()

fixes: #540 closes: #541

Testing - to be on the safe side:

• [x] https://jenkins.scylladb.com/job/scylla-staging/job/dtest-pytest-gating/340/ (OSS)
• [x] https://jenkins.scylladb.com/job/scylla-staging/job/dtest-pytest-gating/341/ (Enterprise)

[tchaikov]

might want to reference #541.

[fruch]

might want to reference #541.

yeah, I forgot @eliransin was trying to solved it in #541 now that I look at it, it's similar but a bit longer than this one

[fruch]

Looks good to me. I assumed you tested it actually works? :-)

it works for the cases reported, i.e. multiple --experimental-features

[fruch]

tests showed, that a few places were needed to change and expect a list, not assume an int.

fixed those and re-running gating

[fruch]

Code is failing in gating

Need to check why it's still breaking Scylla boot

[bhalevy]

@nyh by the way, why don't we support comma-separated list arg in scylla --experimental-features?

[nyh]

I don't know (I don't think I wrote that code?), we definitely could. But we need to also keep supporting the current approach (multiple instances of the option), because it's convenient in scripts.

[fruch]

Code is failing in gating

Need to check why it's still breaking Scylla boot

found the issue, the args without value, was passing empty space as value (it wasn't clear from logs) now fixe, and giving one more go in gating