virConnectOpenInternal: Avoid double free() when alias is an invalid URI

virConnectOpenInternal: Avoid double free() when alias is an invalid URI

Configuring an URI alias such as

  uri_aliases = [
      "blah=qemu://invaliduri@@@",
  ]

Results in a double free when the alias is used:

  $ virsh -c blah
  free(): double free detected in tcache 2
  Aborted (core dumped)

This happens as the 'alias' variable is first assigned to 'uristr' which
is cleared in the 'failed' label and then is explicitly freed again.

Fix this by stealing the alias into 'uristr' and removing the
unnecessary freeing.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>