[remote-run] Clear out %t on the remote machine

Really we ought to clear out "%t*", but running wildcards with 'rm'
scares me a little too much for that. This still fixes a handful of
tests that were relying on %t being an empty directory.

Note that this doesn't interfere with generated files persisting
between %target-run invocations; they'll be downloaded and then
re-uploaded as long as they're mentioned in the invocation.

Author: jrose-apple

test/remote-run/custom-options.test-sh

@@ -3,6 +3,11 @@ RUN: %utils/remote-run -n --remote-dir /xyz-REMOTE -o FIRST_OPT -o SECOND_OPT --
 CHECK: /usr/bin/ssh -n
 CHECK-DAG: -p 12345
 CHECK-DAG: -o FIRST_OPT -o SECOND_OPT
+CHECK-SAME: some_user@some_host -- '/usr/bin/env' '/bin/rm' '-rf' '{{.+}}-REMOTE/output'
+
+CHECK-NEXT: /usr/bin/ssh -n
+CHECK-DAG: -p 12345
+CHECK-DAG: -o FIRST_OPT -o SECOND_OPT
 CHECK-SAME: some_user@some_host -- '/usr/bin/env' '/bin/mkdir' '-p' '{{.+}}-REMOTE/output/nested'
 
 CHECK-NEXT: /usr/bin/sftp

test/remote-run/identity.test-sh

@@ -3,6 +3,11 @@ RUN: %utils/remote-run -n --remote-dir /xyz-REMOTE -i spiderman --output-prefix
 CHECK: /usr/bin/ssh -n
 CHECK-DAG: -p 12345
 CHECK-DAG: -i spiderman
+CHECK-SAME: some_user@some_host -- '/usr/bin/env' '/bin/rm' '-rf' '{{.+}}-REMOTE/output'
+
+CHECK-NEXT: /usr/bin/ssh -n
+CHECK-DAG: -p 12345
+CHECK-DAG: -i spiderman
 CHECK-SAME: some_user@some_host -- '/usr/bin/env' '/bin/mkdir' '-p' '{{.+}}-REMOTE/output/nested'
 
 CHECK-NEXT: /usr/bin/sftp

utils/remote-run

@@ -28,7 +28,7 @@ class CommandRunner(object):
 
     @staticmethod
     def _dirnames(files):
-        return list(set(os.path.dirname(f) for f in files))
+        return sorted(set(os.path.dirname(f) for f in files))
 
     def popen(self, command, **kwargs):
         if self.verbose:
@@ -195,23 +195,32 @@ def main():
     runner.dry_run = args.dry_run
     runner.verbose = args.verbose or args.dry_run
 
+    assert not args.remote_dir == '/'
+
     upload_files = dict()
     download_files = dict()
+    remote_test_specific_dir = None
     if args.input_prefix:
+        assert not args.remote_input_prefix.startswith("..")
         remote_dir = os.path.join(args.remote_dir, args.remote_input_prefix)
         input_files = find_transfers(args.command, args.input_prefix, 
                                      remote_dir)
         assert not any(upload_files.has_key(f) for f in input_files)
         upload_files.update(input_files)
     if args.output_prefix:
+        assert not args.remote_output_prefix.startswith("..")
         remote_dir = os.path.join(args.remote_dir, args.remote_output_prefix)
         test_files = find_transfers(args.command, args.output_prefix, 
                                     remote_dir)
         assert not any(upload_files.has_key(f) for f in test_files)
         upload_files.update(test_files)
         assert not any(download_files.has_key(f) for f in test_files)
         download_files.update(test_files)
+        remote_test_specific_dir = remote_dir
 
+    if remote_test_specific_dir:
+        assert remote_test_specific_dir.startswith(args.remote_dir)
+        runner.run_remote(['/bin/rm', '-rf', remote_test_specific_dir])
     if upload_files:
         runner.send(upload_files)