Running under python 3, the response from running the `bw` command is a
byte string, so the lookup was returning to ansible values of the form
`b'somestring'`. It is necessary to decode these results.
This makes it easier to look up the values of custom fields in a
Bitwarden entry. If the `custom_field` named parameter is true, search
for the named `field` in the list of custom fields rather than the
top-level dictionary.
