matroskamux: Add property to set DateUTC

Add a property that makes it possible for an application to set the
DateUTC header field in matroska files. This is useful for live feeds,
where the DateUTC header can be set to a UTC timestamp, matching the
beginning of the file.

Fixes gstreamer/gst-plugins-good#481
24 jobs for matroskadateutc in 68 minutes and 20 seconds (queued for 16 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #636897
gst indent

00:00:30

passed #636896
manifest

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  Build
passed #636907
build cerbero cross-android universal

00:17:46

manual #636911
gst-ios-12.2 allowed to fail manual
build cerbero cross-ios universal
passed #636908
build cerbero cross win32

00:12:09

passed #636909
build cerbero cross win64

00:09:40

passed #636906
build cerbero fedora x86_64

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passed #636910
gst-macos-10.14
build cerbero macos x86_64

00:17:18

passed #636902
build clang fedora x86_64

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passed #636898
build fedora x86_64

00:06:10

passed #636905
docker windows 1607
build msys2

00:11:44

passed #636899
build nodebug fedora x86_64

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passed #636900
build static fedora x86_64

00:14:05

passed #636901
build static nodebug fedora x86_64

00:04:36

passed #636903
docker windows 1607
build vs2017 amd64

00:12:02

passed #636904
docker windows 1607
build vs2017 x86

00:10:54

 
  Test
failed #636912
check fedora

00:04:46

failed #636913
integration testsuites fedora

00:53:11

passed #636915
valgrind bad

00:06:48

passed #636916
valgrind ges

00:09:35

failed #636914
valgrind good

00:10:16

 
  Integrate
passed #636917
cross-android universal examples

00:08:12

skipped #636919
gst-ios-12.2 allowed to fail manual
cross-ios universal examples
passed #636918
documentation

00:04:59

 
Name Stage Failure
failed
integration testsuites fedora Test
           Total: 1451
Uploading artifacts...
gst-build/build/meson-logs/: found 2 matching files
validate-logs: found 70311 matching files

Uploading artifacts to coordinator... ok
id=636913 responseStatus=201 Created token=1KqyxMqC
Uploading artifacts...
validate-logs/*.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=636913 responseStatus=201 Created token=1KqyxMqC
ERROR: Job failed: exit code 1
failed
valgrind good Test
           Total: 679
Uploading artifacts...
gst-build/build/meson-logs/: found 2 matching files
validate-logs: found 1456 matching files

Uploading artifacts to coordinator... ok
id=636914 responseStatus=201 Created token=xrA3ruZ7
Uploading artifacts...
validate-logs/*.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=636914 responseStatus=201 Created token=xrA3ruZ7
ERROR: Job failed: exit code 1
failed
check fedora Test
           Total: 3137
Uploading artifacts...
gst-build/build/meson-logs/: found 2 matching files
validate-logs: found 3556 matching files

Uploading artifacts to coordinator... ok
id=636912 responseStatus=201 Created token=7fQroM-N
Uploading artifacts...
validate-logs/*.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=636912 responseStatus=201 Created token=7fQroM-N
ERROR: Job failed: exit code 1