"Fix" kisNodeModelTest

The KisNodeModelTest didn't set the image it was testing with on
the document. This broke in KisShapeController::setImage(KisImageWSP image),
which cleared all connections, then didn't use the image parameter
but the local doc's image object (which is 0) to reconnect the signals/slots,
and which then crashed in KisShapeController::slotUpdateDocumentResolution(),
where the image would still be 0.

Howewever, the question is: should this function even have this parameter?
If so, should the image then be set on the doc? Should this function even
exist since it makes it possible to have a local m_doc->image() that is
different from the image parameter?

There are still a bunch of warnings, too.

boud@boud-ThinkPad-T470p:~/dev/b-krita/libs/ui/tests$ ./kis_node_model_test

• Start testing of KisNodeModelTest *****

Config: Using QtTest library 5.12.3, Qt 5.12.3 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 7.4.0)
PASS : KisNodeModelTest::initTestCase()
QWARN : KisNodeModelTest::testSetImage() KoColor debug runtime checks are active.
PASS : KisNodeModelTest::testSetImage()
QWARN : KisNodeModelTest::testAddNode() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testAddNode() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testAddNode() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testAddNode() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testAddNode() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
PASS : KisNodeModelTest::testAddNode()
QWARN : KisNodeModelTest::testRemoveAllNodes() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveAllNodes() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveAllNodes() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveAllNodes() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveAllNodes() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
PASS : KisNodeModelTest::testRemoveAllNodes()
QWARN : KisNodeModelTest::testRemoveIncludingRoot() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveIncludingRoot() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveIncludingRoot() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveIncludingRoot() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
QWARN : KisNodeModelTest::testRemoveIncludingRoot() SAFE ASSERT (krita): "!newNode->parent()" in file /home/boud/dev/krita/libs/image/kis_node.cpp, line 500
PASS : KisNodeModelTest::testRemoveIncludingRoot()
PASS : KisNodeModelTest::cleanupTestCase()
Totals: 6 passed, 0 failed, 0 skipped, 0 blacklisted, 1597ms

• Finished testing of KisNodeModelTest *****