Fix key ID processing

Fix key ID processing

If ns1/setup.sh generates a key with ID 0, the "KEYID" token in
ns1/named.conf.in will be replaced with an empty string, causing the
following broken statement to appear in ns1/named.conf:

    tkey-dhkey "server" ;

Such a statement triggers false positives for the "tkey" system test due
to ns1 being unable to start with a broken configuration file.  Fix by
tweaking the regular expression used for removing leading zeros from the
key ID, so that it removes at most 4 leading zeros.