s3: fix minimum botocore version
s3: fix minimum botocore version

Botocore is mainly used as a dependency of boto3, but Gnocchi actually requires
version 1.5 minimum to have list_objects_v2 available.

Change-Id: Ie5e4760c630d9906b57eda48dbd42165108c96e7

sileht/gnocchi,leandroreox/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,gnocchixyz/gnocchi