Merge #21004: contrib: Fix docker args conditional in gitian-build

624091b7b9 Fix docker args conditional (setpill)

Pull request description:

  The conditional that checks if docker needs to be installed has the side effect of triggering the default `lxc` branch in case docker comes preinstalled. This is clearly not intentional.

ACKs for top commit:
  laanwj:
    Code review ACK 624091b7b9
  theStack:
    Code review ACK 624091b7b9

Tree-SHA512: e37e2c35aaed813762223e5963e5416d5865b3fb53efb2aac86daaa03b95ccf07db9c3a779446029d055ab89491147c4d900117273e22caed201b21bdf287c58

contrib/gitian-build.py

@@ -13,15 +13,16 @@ def setup():
     programs = ['ruby', 'git', 'make', 'wget', 'curl']
     if args.kvm:
         programs += ['apt-cacher-ng', 'python-vm-builder', 'qemu-kvm', 'qemu-utils']
-    elif args.docker and not os.path.isfile('/lib/systemd/system/docker.service'):
-        dockers = ['docker.io', 'docker-ce']
-        for i in dockers:
-            return_code = subprocess.call(['sudo', 'apt-get', 'install', '-qq', i])
-            if return_code == 0:
-                break
-        if return_code != 0:
-            print('Cannot find any way to install Docker.', file=sys.stderr)
-            sys.exit(1)
+    elif args.docker:
+        if not os.path.isfile('/lib/systemd/system/docker.service'):
+            dockers = ['docker.io', 'docker-ce']
+            for i in dockers:
+                return_code = subprocess.call(['sudo', 'apt-get', 'install', '-qq', i])
+                if return_code == 0:
+                    break
+            if return_code != 0:
+                print('Cannot find any way to install Docker.', file=sys.stderr)
+                sys.exit(1)
     else:
         programs += ['apt-cacher-ng', 'lxc', 'debootstrap']
     subprocess.check_call(['sudo', 'apt-get', 'install', '-qq'] + programs)