snapcraft for maven project included setuid binary

I'm reporting this bug on behalf of someone in an email thread.

Currently, snaps are not allowed to ship setuid/setgid binaries. It isn't supported by the snappy install operation and the security policy does not allow CAP_SETUID and CAP_SETGID, so the review tools check for this to make sure everything is ok. (Perhaps one day we will want to support this, but IMO we should avoid this for as long as possible and very carefully think about how to support it (if at all) because things could get complicated in a hurry on a system like Ubuntu Personal.)

In that spirit, snapcraft for maven projects is pulling in fusermount and the review tools complains:
found errors in hashes.yaml: mode 'rwxr-xr-x' != 'rwsr-xr-x' for 'bin/fusermount', mode 'rwxr-xr-x' != 'rwsr-xr-x' for 'usr/lib/eject/dmcrypt-get-device' lint_file_mode

Snapcraft should strip the setuid/setgid bits of any files before calling snappy build.