Before revision:  A priori and  {\it a posteriori} energy norm analysis is established for a sufficiently large penalization parameter and  sufficiently fine triangulation . Optimal order a priori error estimates in L^2 norm is also established.
After revision:  A priori and {\it a posteriori} energy norm analysis is established for a sufficiently large penalization parameter and sufficiently fine triangulation  a priori error estimates in L^2 norm is also established.