rebasing back from container to pure ostree fails

[cgwalters]

# rpm-ostree rebase --experimental ostree-unverified-registry:quay.io/coreos-assembler/fcos:stable
...
# rpm-ostree rebase fedora:fedora/x86_64/coreos/testing-devel
error: Invalid refspec ostree-unverified-registry:quay.io/coreos-assembler/fcos:stable

This is a bug in the rebase code, we shouldn't be trying to interpret the prior refspec as ostree.

[lucab]

I took some time to identify where this is coming from, and it looks like the error is originating here:

rpm-ostree/src/daemon/rpmostreed-transaction-types.cxx

Lines 86 to 90 in 730bec8

	/* The rest of the code assumes TYPE_OSTREE refspec */
	g_autofree gchar *new_refspec = NULL;
	if (!rpmostreed_refspec_parse_partial (refspec, current_refspec.refspec.c_str (), &new_refspec,
	error))
	return FALSE;

And we are reaching there through this:

rpm-ostree/src/daemon/rpmostreed-transaction-types.cxx

Lines 301 to 306 in 730bec8

	if (self->refspec != NULL)
	{
	if (!change_origin_refspec (NULL, sysroot, origin, self->refspec, cancellable, NULL, NULL,
	error))
	return FALSE;
	}