List.find_all is a synonym for List.filter and doesn't throw
List.find_all is a synonym for List.filter and doesn't throw

Replace it with List.filter (more common), and remove the redundant
exception try/with.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@citrix.com>

simonjbeaumont/mirage-block-volume,djs55/mirage-block-volume