[zombienet] Disable tests

[pepoviola]

This pr remove rococo-parachain and makes penpal-parachain the default one to use (if not chain is passed), but zombienet isn't working out-of-the-box with that para (yet paritytech/zombienet-sdk#480). The affected tests are:

• zombienet-polkadot-shared-core-idle-parachain
• zombienet-polkadot-functional-async-backing-6-seconds-rate
• zombienet-polkadot-elastic-scaling-doesnt-break-parachains
• zombienet-polkadot-smoke-0005-precompile-pvf-smoke
• zombienet-polkadot-smoke-0004-coretime-smoke-test
• zombienet-polkadot-smoke-0002-parachains-parachains-upgrade-smoke