utils/genrandconfig: do not use BR2_BACKUP_SITE for some builds

In order to test that upstream sites are still working, we need to NOT
fallback to sources.buildroot.net for some builds.

As there is anyway a local cache in the autobuilder instances, we need
to do quite a lot of builds without any BR2_BACKUP_SITE configured to
have a chance to catch issues, which is why a 50% chance is used to
unset BR2_BACKUP_SITE.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit da5c25c9f91b17a3c00ff0b35164881f2d1aa425)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

utils/genrandconfig

@@ -555,6 +555,11 @@ async def gen_config(args):
         configlines.append("BR2_REPRODUCIBLE=y\n")
         configlines.append("BR2_TARGET_ROOTFS_TAR=y\n")
 
+    # From time to time, ignore sources.buildroot.net to really fetch
+    # from upstream
+    if randint(0, 1) == 0:
+        configlines.append("""BR2_BACKUP_SITE=""\n""")
+
     with open(configfile, "a") as configf:
         configf.writelines(configlines)