terrasync.py: use os.path.abspath() in TerraSync.setTarget()

Using os.path.abspath() here in TerraSync.setTarget() adds a safety
layer in case the process later calls os.chdir() or similar[1], which
would change the meaning of the "." directory. Also remove the strip()
call which I don't consider useful here, see my message at:

  https://sourceforge.net/p/flightgear/mailman/message/36208140/

[1] Not the case currently, but who knows what will happen in the
    future...

scripts/python/terrasync.py

@@ -507,7 +507,9 @@ class TerraSync:
         return self
 
     def setTarget(self, target):
-        self.target = target.rstrip('/').strip()
+        # Using os.path.abspath() here is safer in case the process later uses
+        # os.chdir(), which would change the meaning of the "." directory.
+        self.target = os.path.abspath(target)
         return self
 
     def start(self):