test_140_kernel_modules_not_tainted in ubuntu_qrt_kernel_security failed on Trusty ARM64

This was reported in bug 1630000
I think it's better it tear it down into pieces.

  FAIL: test_140_kernel_modules_not_tainted (__main__.KernelSecurityTest)
  kernel modules are not marked with a taint flag (especially 'E' for TAINT_UNSIGNED_MODULE)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "./test-kernel-security.py", line 1727, in test_140_kernel_modules_not_tainted
      self.fail('Module \'%s\' is tainted: %s' % (fields[0], last_field))
  AssertionError: Module 'signpost' is tainted: (OX)

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.13.0-141-generic 3.13.0-141.190
ProcVersionSignature: User Name 3.13.0-141.190-generic 3.13.11-ckt39
Uname: Linux 3.13.0-141-generic aarch64
AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access /dev/snd/: No such file or directory
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.14.1-0ubuntu3.27
Architecture: arm64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
CRDA: Error: [Errno 2] No such file or directory: 'iw'
Date: Wed Feb 7 07:21:29 2018
Lsusb: Error: command ['lsusb'] failed with exit code 1: unable to initialize libusb: -99
PciMultimedia:

ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB:

ProcKernelCmdLine: console=ttyS0,9600n8r ro
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-141-generic N/A
 linux-backports-modules-3.13.0-141-generic N/A
 linux-firmware 1.127.24
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)