resolved: log error messages for openssl/gnutls context creation

resolved: log error messages for openssl/gnutls context creation

In https://bugzilla.redhat.com/show_bug.cgi?id=2322937 we're getting
an error message:
Okt 29 22:21:03 fedora systemd-resolved[29311]: Could not create manager: Cannot allocate memory
I expect that this actually comes from dnstls_manager_init(), the
openssl version. But without real logs it's hard to know for sure.

Use EIO instead of ENOMEM, because the problem is unlikely to be actually
related to memory.

(cherry picked from commit ee95e86ae163e436384f1b782a77a7e18deba890)