Add the ansible_2_10 intersphinx reference. (#71028)

There are links from the scenario guides to collections but collections
docs aren't built in testing or locally when we're on the devel branch.
Due to that we need to make sure those references resolve to the
production docsite.  We can use intersphinx to make sure that happens.

* The test for binary files wasn't reading enough of the file.

Checking for null bytes in the first 1024 bytes failed to diagnose the
ansible_2_10.inv file as binary

docs/docsite/rst/conf.py

@@ -280,6 +280,7 @@ autoclass_content = 'both'
 intersphinx_mapping = {'python': ('https://docs.python.org/2/', (None, '../python2.inv')),
                        'python3': ('https://docs.python.org/3/', (None, '../python3.inv')),
                        'jinja2': ('http://jinja.palletsprojects.com/', (None, '../jinja2.inv')),
+                       'ansible_2_10': ('https://docs.ansible.com/ansible/2.10/', (None, '../ansible_2_10.inv')),
                        'ansible_2_9': ('https://docs.ansible.com/ansible/2.9/', (None, '../ansible_2_9.inv')),
                        'ansible_2_8': ('https://docs.ansible.com/ansible/2.8/', (None, '../ansible_2_8.inv')),
                        'ansible_2_7': ('https://docs.ansible.com/ansible/2.7/', (None, '../ansible_2_7.inv')),

test/lib/ansible_test/_internal/util.py

@@ -500,7 +500,7 @@ def is_binary_file(path):
 
     with open_binary_file(path) as path_fd:
         # noinspection PyTypeChecker
-        return b'\0' in path_fd.read(1024)
+        return b'\0' in path_fd.read(2048)
 
 
 def generate_password():