Scylla startup fails with an error if "-c" or "-m" is used in `SCYLLA_EXT_OPTS`

[eliransin]

It looks like ccm is unaware of the abbreviations for --smp and --memory (-c and -m) , this causes scylla startup to
fail with an error about same command line option for smp or/and memory being given twice.

Way to reproduce:
try to create and start a scylla cluster using export SCYLLA_EXT_OPTS="-c 2"

Scylla will fail with an error about duplicate command line options.

[cezarmoise]

@fruch should this be closed due to #558?

[fruch]

@fruch should this be closed due to #558?

Maybe, I have't tested this specific case.