tests/acceptance: skip LinuxInitrd 2gib with v4.16 on GitLab

This fails on GitLab but not when run locally on the same container
image. It's very confusing.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200701135652.1366-30-alex.bennee@linaro.org>

tests/acceptance/linux_initrd.py

@@ -8,10 +8,12 @@
 # This work is licensed under the terms of the GNU GPL, version 2 or
 # later.  See the COPYING file in the top-level directory.
 
+import os
 import logging
 import tempfile
 
 from avocado_qemu import Test
+from avocado import skipIf
 
 
 class LinuxInitrd(Test):
@@ -51,6 +53,7 @@ class LinuxInitrd(Test):
                 max_size + 1)
             self.assertRegex(self.vm.get_log(), expected_msg)
 
+    @skipIf(os.getenv('GITLAB_CI'), 'Running on GitLab')
     def test_with_2gib_file_should_work_with_linux_v4_16(self):
         """
         QEMU has supported up to 4 GiB initrd for recent kernel