logind: improve logging in manager_connect_console()

logind: improve logging in manager_connect_console()

let's make sure we log about every failure

Also, complain about systems where /dev/tty0 exists but
/sys/class/tty/tty0/active does not. Such systems (usually container
environments) are pretty broken as they mount something that is not a VC
to /dev/tty0 and they really shouldn't.

Systems should either have a VC or not, but not badly fake one by
mounting things wildly.

This just adds a warning message, as before we'll simply turn off VC
handling in this case.

(cherry picked from commit 0b6d55cae9b8adc507fbea95d1b2874729a77386)

Related: #1642460