Fix bad pattern used in CLI argument parsing

[fmassot]

As suggested by @guilload

Would be better to use this pattern:

let metastore_uri = matches
    .value_of("metastore-uri")
    .map(normalize_uri)
    .expect("`metastore-uri` should be a required arg.")?;

[fulmicoton]

I thinnk we already do that. Should we close?