IMPALA-575: CREATE TABLE should validate directory permissions/existence as part of
LOCATION path analysis checks and show warnings.

If the location path in DDL does not exist or Impala cannot access it, we should
show a warning to user so they could verify if there is a typo in DDL stmt location
part. Sometimes user creates table to read data inserted by other tools and does not
need write access, it's good to return a warning so user is aware of permission.

Change-Id: Ic82facd0099c452e7e26ea0f5846f9c59bf63571
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5466
Reviewed-by: Juan Yu <jyu@cloudera.com>
Tested-by: jenkins