update mysqlcppconn url

Change-Id: I96579ed4be05cc22bc66f80bd39d7af961d47470
remove some external header guards

Change-Id: I5a51dc496835f0998a3422f2a1f0f2ff8bb3c13f
fix include guard for sal/types.h

Change-Id: I77e10d2644b18b150f9489c7f754405974af107a