tests.py: add --jobs command line parameter
tests.py: add --jobs command line parameter

Allowing for setting the number of jobs to use for running the tests.

Signed-off-by: Botond Dénes <a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>
Message-Id: <d58d6393c6271bffc37ab3b5edc37b00ef485d9c.1529433590.git.a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>

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