ganeti.http: Handle SSL_ERROR_ZERO_RETURN
ganeti.http: Handle SSL_ERROR_ZERO_RETURN

Also add a comment next to the place where the SSL connection is shut
down.

Reviewed-by: iustinp


dimara/ganeti,apyrgio/ganeti,leshchevds/ganeti,ganeti/ganeti,mbakke/ganeti,dimara/ganeti,andir/ganeti,apyrgio/snf-ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,yiannist/ganeti,andir/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,andir/ganeti,mbakke/ganeti,onponomarev/ganeti,leshchevds/ganeti,mbakke/ganeti,apyrgio/ganeti,yiannist/ganeti,yiannist/ganeti,bitemyapp/ganeti,grnet/snf-ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,leshchevds/ganeti,bitemyapp/ganeti