IMPALA-1059: Backtick argument passed to USE by shell -d option

If not backticked, arguments such as parquet are interpreted as
keywords, when it is possible a database by that name exists.

This could have been avoided via single quotes around backticks: -d '`parquet`'
Otherwise, -d `parquet` throws a commandline error.

In interactive mode, backticks alone (ex. use `parquet`) will pass the
name as an identifier rather than a keyword.

Change-Id: I24b43eeeb6b4bfda5388165856788a20b64bc2ba
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3307
Reviewed-by: Abdullah Yousufi <abdullah.yousufi@cloudera.com>
Tested-by: jenkins