multitest.py: error if no hosts given

Otherwise it'll just hang waiting for a non-existent host.

Closes: #917
Approved by: cgwalters

tests/vmcheck/multitest.py

@@ -14,6 +14,10 @@ def main():
     for host in sys.argv[1:]:
         hosts.append(Host(host))
 
+    if len(hosts) == 0:
+        print("error: no hosts provided")
+        sys.exit(1)
+
     requested_tests_spec = os.environ.get('TESTS')
     if requested_tests_spec is not None:
         requested_tests = requested_tests_spec.split()