bitbucket-gen-key.sh should be run from the host machine prior to running VVV for the first time.  This is because generating the keys is an interactive process so it can't be done during vagrant provisioning, and provisioning includes scripts which need this key to clone repos from bitbucket. The alternative is to require the user to boot the VM, run the bitbucket-gen-key.sh script there, and then reboot, which seems like more work.
maybe_update_file() function to handle updating/copying files
Using maybe_update_file() to install Bitbucket keys
Set proper permissions for the Bitbucket SSH keys
Use maybe_update_file() for managing wp-config.php