Instana attachpid file removal handling (#1884)

* Fix stale .attach_pid files left in cwd if target process dies before attachment in Hotspot

* Review comments added

* Add ASM URL for copyright note.

* Normalize formatting.

---------

Co-authored-by: krishnapriyars <Krishnapriya.RS@ibm.com>

Author: raphw

byte-buddy-agent/src/main/java/net/bytebuddy/agent/VirtualMachine.java

@@ -564,6 +564,11 @@ public Connection connect(String processId) throws IOException {
                                     throw new IllegalStateException("Could not create attach file: " + attachFile);
                                 }
                             }
+                            try {  // Keep canonical file for cleanup in case target process ends and /proc/<pid>/cwd link disappears
+                                attachFile = attachFile.getCanonicalFile();
+                            } catch (IOException ignored) {
+                                /* do nothing */
+                            }
                             try {
                                 kill(processId, 3);
                                 int attempts = this.attempts;