[LNT][NFC] Fix global import in function

Summary:
The _load_dependencies() function in lnt.lnttool.admin import some
modules in the global namespace by making the module name global and
then doing imports. However the language reference for global statements
forbids this:

"Names listed in a global statement must not be defined as formal
parameters or in a for loop control target, class definition, function
definition, or import statement."

This commit makes use of importlib.import_module wrapper instead of the
import statement to respect this restriction.

Reviewers: cmatthews, hubert.reinterpretcast, kristof.beyls, PrzemekWirkus

Reviewed By: PrzemekWirkus

Subscribers: PrzemekWirkus, leandron, MatzeB, llvm-commits

Differential Revision: https://reviews.llvm.org/D68779

Author: Thomas Preud'homme

lnt/lnttool/admin.py

@@ -2,17 +2,18 @@
 from future import standard_library
 standard_library.install_aliases()
 import click
+from importlib import import_module
 from .common import submit_options
 
 
 def _load_dependencies():
     global yaml, sys, requests, json, os, http
-    import yaml
-    import sys
-    import requests
-    import json
-    import os
-    import http.client
+    yaml = import_module('yaml')
+    sys = import_module('sys')
+    requests = import_module('requests')
+    json = import_module('json')
+    os = import_module('os')
+    http = import_module('http.client')
 
 
 def _error(msg):