daemon/worker: fixes for handling of some non-fatal TLS errors, metrics

daemon/worker: fixes for handling of some non-fatal TLS errors, metrics

The handshake now properly deals with GNUTLS_E_INTERRUPTED to retry,
and GNUTLS_E_WARNING_ALERT_RECEIVED and GNUTLS_E_GOT_APPLICATION_DATA
during session resumption.

Added a metric for monitoring TLS handshake errors.

Added `net.tls_handshake_timeout([milliseconds])` for configurable
TLS handshake timeout (default is 6000ms), and documentation for
`net.tcp_in_idle([milliseconds])`.