Thread.h: disable copy constr and assignment op

Disable copy constructor and assignment operator.
They are currently not defined, so any attempt to use them will
result in linker error.

Signed-off-by: Michal Jarzabek <stiopa@gmail.com>

src/common/Thread.h

@@ -29,8 +29,8 @@ class Thread {
   void *entry_wrapper();
 
  public:
-  explicit Thread(const Thread& other);
-  const Thread& operator=(const Thread& other);
+  Thread(const Thread&) = delete;
+  Thread& operator=(const Thread&) = delete;
 
   Thread();
   virtual ~Thread();