Use and_then to streamline control flow in get_metadata
Use and_then to streamline control flow in get_metadata

This function does a series of things that if any one goes wrong it
continues. Another way to express this is as a series of dependent
operations with and_then.

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

mulkieran/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,mulkieran/stratisd,trgill/stratisd,stratis-storage/stratisd,trgill/stratisd