element: Enforce that elements created by gst_element_factory_create/make() are floating

Bindings might have a hard time making sure that the reference is indeed
still floating after returning here.

See gstreamer/gstreamer#444
24 jobs for backport-mr-284-into-1.16-device-create-element in 44 minutes and 36 seconds (queued for 7 seconds)
Status Job ID Name Coverage
  Preparation
passed #608768
gst indent

00:00:29

passed #608767
manifest

00:00:39

 
  Build
passed #608777
build cerbero android universal

00:13:32

passed #608778
build cerbero cross win32

00:09:06

passed #608779
build cerbero cross win64

00:06:52

passed #608776
build cerbero fedora x86_64

00:08:14

passed #608781
gst-ios-12.2
build cerbero ios universal

00:43:53

passed #608780
gst-macos-10.14
build cerbero macos x86_64

00:07:22

passed #608769
build fedora x86_64

00:09:15

passed #608775
docker windows 1607
build msys2

00:11:30

passed #608770
build nodebug fedora x86_64

00:08:15

passed #608771
build static fedora x86_64

00:13:50

passed #608772
build static nodebug fedora x86_64

00:05:29

passed #608773
docker windows 1607
build vs2017 amd64

00:09:21

passed #608774
docker windows 1607
build vs2017 x86

00:09:51

 
  Test
passed #608782
check fedora

00:06:38

passed #608783
integration testsuites fedora

00:12:50

passed #608788
valgrind bad

00:11:10

passed #608785
valgrind base

00:11:59

passed #608784
valgrind core

00:28:19

passed #608789
valgrind ges

00:04:05

passed #608786
valgrind good

00:09:10

passed #608787
valgrind ugly

00:04:44

 
  Integrate
passed #608790
android universal examples

00:09:48