Remove existing thread state for clone children

When parsing clone exit events, specifically for the child half of a
clone and when in a container, always remove any existing thread state
that may be attached to the event and remove that state from the thread
manager.

This matches the logic on the parent side, which is to let the child
create the thread.

This ensures that if there does happen to be an existing thread state
from an old thread that happened to share the same thread id, that it
will be removed.

This fixes #664.

userspace/libsinsp/parsers.cpp

@@ -947,6 +947,22 @@ void sinsp_parser::parse_clone_exit(sinsp_evt *evt)
 	{
 		//
 		// clone() returns 0 in the child.
+		//
+
+		//
+		// If the threadinfo in the event exists, and we're in
+		// a container, the threadinfo in the event must be
+		// stale (e.g. from a prior process with the same
+		// tid), because only the child side of a clone
+		// creates the threadinfo for the child. Clear and
+		// remove the old threadinfo.
+		//
+		if(evt->m_tinfo && in_container)
+		{
+			m_inspector->remove_thread(tid, true);
+			evt->m_tinfo = NULL;
+		}
+
 		// Validate that the child thread info has actually been created.
 		//
 		if(!evt->m_tinfo)
@@ -998,17 +1014,8 @@ void sinsp_parser::parse_clone_exit(sinsp_evt *evt)
 		else
 		{
 			//
-			// We are in the child's clone. If we are in a container, make
-			// sure the vtid/vpid are reflected because the father was maybe
-			// running outside the container so created the child thread without
-			// knowing the internal vtid/vpid
+			// Let the parent create the threadinfo for the child
 			//
-			if(in_container)
-			{
-				evt->m_tinfo->m_vtid = vtid;
-				evt->m_tinfo->m_vpid = vpid;
-			}
-
 			return;
 		}
 	}