First choice of replica for given external dictionary should be based on randomness instead of order in configuration file.

#include <mysqlxx/PoolWithFailover.h>
static bool startsWith(const std::string & s, const char * prefix)
{
    return s.size() >= strlen(prefix) && 0 == memcmp(s.data(), prefix, strlen(prefix));
}
using namespace mysqlxx;
PoolWithFailover::PoolWithFailover(const Poco::Util::AbstractConfiguration & config_,