IMPALA-3866: consistent user-facing terminology for scratch dirs
IMPALA-3866: consistent user-facing terminology for scratch dirs

Error messages inconsistently referred to "temporary" versus "scratch".
Make the error messages consistent to make it easier for users to debug.
Also make sure the --scratch_dirs configuration option is always
mentioned.

Change-Id: I011e633721e206a2b6ecf1c34d5328f34fbc01ab
Reviewed-on: http://gerrit.cloudera.org:8080/3805
Reviewed-by: Matthew Jacobs <df2fa7c39d141dc5dc5589fed74180e757ed6c9a@cloudera.com>
Reviewed-by: Dan Hecht <20ebd99959f0f6e5dcb0fc319b4d8ef53a16b5fb@cloudera.com>
Reviewed-by: Marcell Szabo <f0b0a766c24b566b1711dadb7c01a32650701ad6@cloudera.com>
Tested-by: Internal Jenkins

michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala