rtpbin: add request-jitterbuffer signal

This can be used to pass the threadsharing jitterbuffer from
gst-plugins-rs for example.
24 jobs for rtpbin-request-jb in 167 minutes and 18 seconds (queued for 17 seconds)
Status Job ID Name Coverage
  Preparation
passed #651907
gst indent

00:00:43

passed #651906
manifest

00:00:55

 
  Build
passed #651917
build cerbero cross-android universal

00:14:08

manual #651921
gst-ios-12.2 allowed to fail manual
build cerbero cross-ios universal
passed #651918
build cerbero cross win32

00:09:54

passed #651919
build cerbero cross win64

00:07:07

failed #651916
build cerbero fedora x86_64

00:03:59

passed #651920
gst-macos-10.14
build cerbero macos x86_64

00:09:20

passed #651912
build clang fedora x86_64

00:06:24

passed #651908
build fedora x86_64

00:06:01

passed #651915
docker windows 1607
build msys2

00:12:32

passed #651909
build nodebug fedora x86_64

00:03:04

passed #651910
build static fedora x86_64

00:13:09

passed #651911
build static nodebug fedora x86_64

00:02:55

passed #651913
docker windows 1607
build vs2017 amd64

00:09:56

passed #651914
docker windows 1607
build vs2017 x86

00:11:42

 
  Test
passed #651922
check fedora

00:03:23

passed #651923
integration testsuites fedora

00:14:48

passed #651925
valgrind bad

00:09:35

passed #651926
valgrind ges

00:09:01

passed #651924
valgrind good

00:13:12

 
  Integrate
passed #651927
cross-android universal examples

00:10:52

skipped #651929
gst-ios-12.2 allowed to fail manual
cross-ios universal examples
passed #651928
documentation

00:05:25

 
Name Stage Failure
failed
build cerbero fedora x86_64 Build
0:01:56 Recipe 'gst-plugins-good-1.0' failed at the build step 'compile'
Fatal Error: Running ['sh', '-c', 'ninja -v -d keeprsp'], returncode 1

Uploading artifacts...
manifest.xml: found 1 matching files
cerbero-build/logs: found 27 matching files

WARNING: *.tar.bz2: no matching files
Uploading artifacts to coordinator... ok
id=651916 responseStatus=201 Created token=He52UZAV
ERROR: Job failed: exit code 1