Don't hard-code temporaryfilename for CA certificate

[mclasmeier]

Part of #91.

This PR also fixes a bug (same bug in multiple lines), where we are doing

env = append(env, fmt.Sprintf("ROX_ENDPOINT=%q", endpoint))

instead of

env = append(env, fmt.Sprintf("ROX_ENDPOINT=%s", endpoint))

resulting in literal quotation characters ending up in the variable values.

[AlexVulaj]

One thing I noticed — cmd/teardown.go also calls deployer.New() (line 43) but doesn't have the deferred Cleanup() that you added to cmd/deploy.go. Might want to add it there too so teardowns don't leak temp dirs.