buildman: Allow skipping of tests which use the network

Accessing the network slows down the test and limits the environment in
which it can be run. Add an option to disable network tests.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/test.py b/tools/buildman/test.py
index 53ebc37..e81400f 100644
--- a/tools/buildman/test.py
+++ b/tools/buildman/test.py
@@ -24,6 +24,8 @@
 import terminal
 import toolchain
 
+use_network = True
+
 settings_data = '''
 # Buildman settings file
 
@@ -410,8 +412,9 @@
 
     def testToolchainDownload(self):
         """Test that we can download toolchains"""
-        self.assertEqual('https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.9.0/x86_64-gcc-4.9.0-nolibc_arm-unknown-linux-gnueabi.tar.xz',
-            self.toolchains.LocateArchUrl('arm'))
+        if use_network:
+            self.assertEqual('https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.9.0/x86_64-gcc-4.9.0-nolibc_arm-unknown-linux-gnueabi.tar.xz',
+                self.toolchains.LocateArchUrl('arm'))
 
 
 if __name__ == "__main__":