cmdline:burn: do not burn options starting --user-*, --password-*

cmdline:burn: do not burn options starting --user-*, --password-*

We have options that start with --user or --password that we don't
want to burn. Some grepping says:

      2 --user1
      1 --user2
     10 --user-allowed-to-authenticate-from
      6 --user-allowed-to-authenticate-to
      2 --user-allow-ntlm-auth
     25 --user-authentication-policy
      1 --user-config
      4 --user-domgroups
      5 --user-ext-name
      2 --user-groups
      6 --user-info
     27 --username
      1 --username2
      2 --userou
      1 --users
      2 --user-sidinfo
      6 --user-sids
     14 --user-tgt-lifetime-mins
      2 --password2
    118 --password-file
      2 --password-from-stdin
      # from here, grepping for strings around POPT_ constants
      5 "user"
      2 "user1"
      2 "user2"
      1 "userd"
      1 "user-domgroups"
      1 "user-groups"
      1 "user-info"
      2 "username"
      1 "user-sidinfo"
      1 "user-sids"
      1 passwordd
      4 "password"

Not all of these use lib/cmdline, but I think most do, via Python
which defers to cmdline_burn().

Note that there are options we should burn that aren't on this list,
like --adminpass. That's another matter.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15674

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Jo Sutton <josutton@catalyst.net.nz>