Bactericidal Activities of Two Daptomycin Regimens against Clinical Strains of Glycopeptide Intermediate-Resistant Staphylococcus aureus , Vancomycin-Resistant Enterococcus faecium , and Methicillin-Resistant Staphylococcus aureus Isolates in an In Vitro Pharmacodynamic Model with Simulated Endocardial Vegetations