Trivial fix to script shebang lines etc. to make them work on FreeBSD

On FreeBSD `burp_ca` and other scripts that the server spawns were not functioning properly because /bin/bash doesn't exist. If you install the `bash` package or port, you get /usr/local/bin/bash instead. The most straightforward way to rectify this issue is to call bash via /usr/bin/env and set the $PATH accordingly to include /usr/local/bin and /usr/local/sbin in the BSD rc.d script.

In addition the the changes above I renamed freebsd/init to a more descriptive (for a BSD person) freebsd/rc.d/burp .