Install and server start scripts should not assume mysql jdbc driver

HCatalog is not limited to mysql (Hive has explicit support for postgres and derby as well) and metastore works with other DB vendors (we are experimenting with Oracle). The mysql driver check gets into the way.

Would also suggest to rename the "DBROOT" variable to "EXTRA_JARS" or something more applicable (it could be any directory with extra jar files required for JDBC or other customization).