Fix problem with bucket existence verification

[davidbnk]

Right now the bash script is using grep to find the presence of the bucket name anywhere in the response of aws s3 ls
The problem is that if you have something like this:

bash# aws s3 ls
2017-02-06 17:55:36 my-bucket-test

And now supose you want to run the script with a bucket named my-bucket, the grep will match the output and it will behave as if the bucket already exists