Update docs and tests for bro_(init|done) -> zeek_(init|done)

testing/btest/scripts/base/protocols/http/content-range-gap-skip.bro

@@ -19,7 +19,7 @@ event content_gap(c: connection, is_orig: bool, seq: count, length: count)
 	got_gap = T;
 	}
 
-event bro_done()
+event zeek_done()
 	{
 	if ( ! got_data_after_gap )
 		exit(1);

testing/btest/scripts/base/protocols/http/http-pipelining.bro

@@ -2,7 +2,7 @@
 # @TEST-EXEC: btest-diff http.log
 
 # mime type is irrelevant to this test, so filter it out
-event bro_init()
+event zeek_init()
 	{
 	Log::remove_default_filter(HTTP::LOG);
 	Log::add_filter(HTTP::LOG, [$name="less-mime-types", $exclude=set("mime_type")]);