Better error message on bootstrap rejected because of blacklist/whitelist

[damip]

2022-12-01T17:38:55.403601Z  INFO massa_node: Node version : TEST.17.0
2022-12-01T17:38:55.435090Z  INFO massa_bootstrap::client: Start bootstrapping from 195.134.167.226:31245
2022-12-01T17:38:55.435808Z  WARN massa_bootstrap::client: Error while bootstrapping: io error: early eof

"early eof" is not very informative of the problem which is lack of whitelisting.

Maybe do it like we do elsewhere: send an error message from the server if there are slots available, otherwise just close