owncloudcmd: fix the --trust  option

We can't call csync_set_userdata in owncloudcmd because it is
going to be overwritten later in the SyncEngine.
So we had an object of type SyncEngine* that we cast to CmdOptions*
and the trust flag was in the padding, so was some random data.

Therefore we must use global variables in that case in order to
know if we should ignore the certificate.