Block /join until nickserv identify has completed when using nickserv auth

[solidgoldbomb]

There is currently an arbitrary 10s delay after identify'ing with nickserv where auth is expected to complete. Sometimes, auth with nickserv takes longer than 10s and the /join may occur before the bot's vhost has been applied by nickserv.

Blocking /join until nickserv auth has completed (when it is enabled) would avoid this issue.

Obviously, this is only relevant when not doing SASL auth.

See #179 for related discussion.