Add option for drop-if-exists when using sqoop hcat import.

To recover from a failed sqoop import via hcat using --create-hcatalog-table, there is a manual step needed to clean up the hive table i.e. (DROP TABLE IF EXISTS <table_name>). It would be great to have another flag --drop-and-create-hcatalog-table, which works like --create-hcatalog-table with an addition of drop if exists before creating the table.