Convert md5 and other checksums to lowercase when setting a location

Now when user wants to set a location to a blob he has to specify at least md5 checksum. In common case the standard doesn't differentiate in what case this string is written. In other words strings '9d385dfdba883dfb789777e77f19310c' are '9D385DFDBA883DFB789777E77F19310C' equal.

Unfortunately for Glare the case the case matters and if it tries to compare to strings from example - it fails. For this reason we need to convert these checksum string to lower case before putting them in store. 'strip' also will be good.

https://github.com/openstack/glare/blob/e25d6605ff381908aadd36436a5005ec96b652fb/glare/engine.py#L272

Instead of 'md5 = blob_meta.pop("md5", None)' there should be

"
try:
    md5 = blob_meta.pop("md5").strip().lower()
except KeyError:
...
"