Fix code comment about IMPALA-2031 (query end time < start time)
Fix code comment about IMPALA-2031 (query end time < start time)

After investigation the issue does not appear to be a bug but a comment
in the code should be update to reflect this.

Change-Id: Ib2e19323729fa6045d89b9b67d40937723b0d032
Reviewed-on: http://gerrit.cloudera.org:8080/535
Reviewed-by: Casey Ching <77bc9a9984e6786c5799d7a71768cf023120ef76@cloudera.com>
Tested-by: Internal Jenkins

kapilrastogi/Impala,brightchen/Impala,theyaa/Impala,bowlofstew/Impala,lnliuxing/Impala,caseyching/Impala,kapilrastogi/Impala,theyaa/Impala,tempbottle/Impala,cchanning/Impala,tempbottle/Impala,rdblue/Impala,gerashegalov/Impala,cgvarela/Impala,bratatidas9/Impala-1,lnliuxing/Impala,theyaa/Impala,caseyching/Impala,theyaa/Impala,gerashegalov/Impala,kapilrastogi/Impala,XiaominZhang/Impala,tempbottle/Impala,lirui-intel/Impala,theyaa/Impala,brightchen/Impala,bratatidas9/Impala-1,rdblue/Impala,kapilrastogi/Impala,lnliuxing/Impala,gerashegalov/Impala,cchanning/Impala,bratatidas9/Impala-1,tempbottle/Impala,rdblue/Impala,XiaominZhang/Impala,cgvarela/Impala,bowlofstew/Impala,brightchen/Impala,brightchen/Impala,bowlofstew/Impala,kapilrastogi/Impala,bratatidas9/Impala-1,caseyching/Impala,XiaominZhang/Impala,caseyching/Impala,rdblue/Impala,theyaa/Impala,lirui-intel/Impala,gerashegalov/Impala,cchanning/Impala,brightchen/Impala,cgvarela/Impala,caseyching/Impala,gerashegalov/Impala,gerashegalov/Impala,kapilrastogi/Impala,rdblue/Impala,brightchen/Impala,bratatidas9/Impala-1,kapilrastogi/Impala,brightchen/Impala,XiaominZhang/Impala,cgvarela/Impala,tempbottle/Impala,lnliuxing/Impala,lirui-intel/Impala,XiaominZhang/Impala,rdblue/Impala,XiaominZhang/Impala,lnliuxing/Impala,caseyching/Impala,cgvarela/Impala,lirui-intel/Impala,lirui-intel/Impala,cgvarela/Impala,theyaa/Impala,bowlofstew/Impala,lirui-intel/Impala,bowlofstew/Impala,XiaominZhang/Impala,tempbottle/Impala,tempbottle/Impala,cchanning/Impala,cchanning/Impala,bowlofstew/Impala,bratatidas9/Impala-1,caseyching/Impala,cchanning/Impala,lnliuxing/Impala,rdblue/Impala,cgvarela/Impala,bratatidas9/Impala-1,gerashegalov/Impala,lirui-intel/Impala,cchanning/Impala,bowlofstew/Impala,lnliuxing/Impala