autobuild-run: handle failed network connection

index 0e12080..350a137 100755
@@ -158,11 +158,15 @@ def log_write(logf, msg):
     logf.flush()
 
 def check_version():
-    with urlopen_closing('http://autobuild.buildroot.org/version') as r:
-        version = int(decode_bytes(r.readline()).strip())
-    if version > VERSION:
-        print("ERROR: script version too old, please upgrade.")
-        sys.exit(1)
+    try:
+        with urlopen_closing('http://autobuild.buildroot.org/version') as r:
+            version = int(decode_bytes(r.readline()).strip())
+        if version > VERSION:
+            print("ERROR: script version too old, please upgrade.")
+            sys.exit(1)
+    except _urllib.URLError:
+        # couldn't check version, assume it's OK
+        pass
 
 class SystemInfo:
     DEFAULT_NEEDED_PROGS = ["make", "git", "gcc", "timeout"]

@@ -242,27 +246,30 @@ def get_toolchain_configs():
     """
     tc_cfg_uri = 'http://autobuild.buildroot.org/toolchains/configs/toolchain-configs.csv'
 
-    with urlopen_closing(tc_cfg_uri) as r:
-        l = decode_byte_list(r.readlines())
-    configs = []
-
-    (_, _, _, _, hostarch) = os.uname()
-    if hostarch == 'i686' or hostarch == 'x86_64':
-        hostarch = 'x86'
-
-    for row in csv.reader(l):
-        config = {}
-        config["url"] = row[0]
-        config["hostarch"] = row[1]
-        # Ignore toolchains that are not built for the appropriate
-        # host architecture
-        if hostarch != config["hostarch"]:
-            continue
-        config["libc"] = row[2]
-        with urlopen_closing(config["url"]) as r:
-            config["contents"] = decode_byte_list(r.readlines())
-        configs.append(config)
-    return configs
+    try:
+        with urlopen_closing(tc_cfg_uri) as r:
+            l = decode_byte_list(r.readlines())
+        configs = []
+
+        (_, _, _, _, hostarch) = os.uname()
+        if hostarch == 'i686' or hostarch == 'x86_64':
+            hostarch = 'x86'
+
+        for row in csv.reader(l):
+            config = {}
+            config["url"] = row[0]
+            config["hostarch"] = row[1]
+            # Ignore toolchains that are not built for the appropriate
+            # host architecture
+            if hostarch != config["hostarch"]:
+                continue
+            config["libc"] = row[2]
+            with urlopen_closing(config["url"]) as r:
+                config["contents"] = decode_byte_list(r.readlines())
+            configs.append(config)
+        return configs
+    except _urllib.URLError:
+        return []
 
 def prepare_build(**kwargs):
     """Prepare for the next build of the specified instance

@@ -471,6 +478,9 @@ def gen_config(**kwargs):
 
     # Select a random toolchain configuration
     configs = get_toolchain_configs()
+    if not configs:
+        log_write(log, "WARNING: no toolchain configurations could be retrieved. Network issue?")
+        return -1
     i = randint(0, len(configs) - 1)
     config = configs[i]