ci_template: avoid exporting the mediafiles into build artifacts

Previously we where accidently exporting the whole repo of
gst-integration-testsuites which includes 350mb of raw media
files and made the artifacts storage explode through the roof
along with the CI bills fd.o had to pay for uploading and
redownloading the artifacts

To deal with this, we clean all the media files from the builddir
and when needed we copy them over from the cache in the docker image,
and then git fetch the repo.

Close #69
40 jobs for master in 33 seconds (queued for 14 seconds)
Status Job ID Name Coverage
  Build Docker
manual #2327768
allowed to fail manual
alpine amd64 manifest builder docker
manual #2327773
allowed to fail manual
android docker
manual #2327772
allowed to fail manual
cerbero fedora amd64 docker
manual #2327771
allowed to fail manual
fedora amd64 docker
manual #2327770
allowed to fail manual
gst-indent amd64 docker
manual #2327769
allowed to fail manual
test manifest amd64 docker
 
  Preparation
passed #2327775
gst indent

00:00:33

manual #2327774
manual
manifest
passed #2327776
test manifest

00:00:17

 
  Build
created #2327786
gstreamer
build cerbero cross-android universal
created #2327799
gst-ios-13.2
build cerbero cross-ios universal
created #2327787
gstreamer
build cerbero cross win32
created #2327788
gstreamer
build cerbero cross win64
created #2327785
gstreamer
build cerbero fedora x86_64
created #2327789
gst-macos-10.15
build cerbero macos x86_64
created #2327781
build clang fedora x86_64
created #2327777
build fedora x86_64
created #2327811
build gst-omx tizonia fedora x86_64
created #2327806
build gst-omx zynq fedora x86_64
created #2327784
docker windows 1809 allowed to fail manual
build msys2
created #2327778
build nodebug fedora x86_64
created #2327779
build static fedora x86_64
created #2327780
build static nodebug fedora x86_64
created #2327782
docker windows 1809
build vs2017 amd64
created #2327783
docker windows 1809 allowed to fail manual
build vs2017 x86
 
  Test
created #2327817
gstreamer
check fedora
created #2327821
gstreamer
integration testsuites fedora 1/4
created #2327822
gstreamer
integration testsuites fedora 2/4
created #2327823
gstreamer
integration testsuites fedora 3/4
created #2327824
gstreamer
integration testsuites fedora 4/4
created #2327829
gstreamer
valgrind bad
created #2327826
gstreamer
valgrind base
created #2327825
gstreamer
valgrind core
created #2327830
gstreamer
valgrind ges
created #2327827
gstreamer
valgrind good
created #2327828
gstreamer
valgrind ugly
 
  Integrate
created #2327832
cross-android universal examples
created #2327834
gst-ios-13.2
cross-ios universal examples
created #2327833
documentation
created #2327831
gstreamer-full