Rework dns_test_makezone()

Rework dns_test_makezone()

The dns_test_makezone() helper function always assigns the created zone
to some view, which is not always necessary and complicates cleanup of
non-managed zones as they are required not to be assigned to any view.

Rework dns_test_makezone() in order to make it easier to use in unit
tests operating on non-managed zones.  Use dns_name_fromstring() instead
of dns_name_fromtext() to simplify code.  Do not use the CHECK() macro
and add comments to make code flow simpler to follow.  Use
dns_test_makeview() instead of dns_view_create().

Adjust existing unit tests using this function so that they still pass.

(cherry picked from commit bfbeef3609dba1929e3df4ab980291a56387006a)
(cherry picked from commit f70c02d2c2a7fe23e045dabe61ff964170ed2f1a)
(cherry picked from commit d45ee39baed24e3d55dfaeb41f26866b2f5d61f1)