Update Python invocations to explicit python3

testing/btest/coverage/find-bro-logs.test

@@ -4,7 +4,7 @@
 #
 # If this test fails, then the "Log Files" documentation page should be updated.
 
-# @TEST-REQUIRES: which python
+# @TEST-REQUIRES: which python3
 # @TEST-EXEC: bash %INPUT
 # @TEST-EXEC: btest-diff out
 
@@ -15,7 +15,7 @@ if [ ! -d "${BROSCRIPTS}" ]; then
     exit 1
 fi
 
-python find_logs.py "${BROSCRIPTS}" | sort > out
+python3 find_logs.py "${BROSCRIPTS}" | sort > out
 
 @TEST-START-FILE find_logs.py
 import os, sys

testing/btest/scripts/base/utils/active-http.test

@@ -1,7 +1,7 @@
-# @TEST-REQUIRES: which python
+# @TEST-REQUIRES: which python3
 # @TEST-REQUIRES: which curl
 #
-# @TEST-EXEC: btest-bg-run httpd python $SCRIPTS/httpd.py --max 2 --addr=127.0.0.1
+# @TEST-EXEC: btest-bg-run httpd python3 $SCRIPTS/httpd.py --max 2 --addr=127.0.0.1
 # @TEST-EXEC: sleep 3
 # @TEST-EXEC: btest-bg-run zeek zeek -b %INPUT
 # @TEST-EXEC: btest-bg-wait 15

testing/scripts/coverage-calc

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # This script aggregates many files containing Zeek script coverage information
 # into a single file and reports the overall coverage information. Usage:

testing/scripts/httpd.py

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 try:
     # Python 2