mysql $UID prefix

We use
${UID}_${PREFIX}
for the first mysql database and ${UID}_ prefix for the additional ones.

the ${UID} value is empty when the first databases is created so the first database name will e wrong.

additional database names are ok.

We need a global prefix which is unique and unchanged in the virtual server lifetime this is why we choose UID. Becasue we can't find any other uniqe and unchangeing id. (normal id is useless unlucky because that's too long, maybe a shorter unique id could be a same good solution in the global variables.)