[#787] Create tempdir in Cleveland if datadir is unspecified

Description

Problem: In cleveland, we are currently defaulting to the user's default tezos-client data directory (i.e. when --cleveland-data-dir isn't specified). In almost all circumstances, this is undesirable: it creates dependency on the environment, can mess up user's data directory, and overall seems like the wrong thing to do.

Solution: If --cleveland-data-dir is unspecified, create a temp. directory and pass it to tezos-client as a datadir. Additional consideration required with setupMoneybagAddress. Have to read secret_keys file to import secret key by alias.

Related issue(s)

Resolves #787 (closed)

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