Code review comment for ~canonical-kernel-team/+git/autotest-client-tests:phlin/bt-log-core

Commit message amended to:
    KERNTT-464
    Add support to read log from journalctl, so that the log check test can
    be run on Ubuntu Core systems.

    The regex must be modified. Here is an example of WARNING taken from
    the syslog of a Google n2d-standard-64 instance:

      May 7 01:50:37 f-l-gen-s2-n2dstd64-u-boot kernel: [ 181.781750] WARNING: CPU: 58 PID: 3002 at kernel/dma/direct.c:35 report_addr+0x37/0x60

    Here is the output of journalctl on this instance:

      May 07 01:50:37 f-l-gen-s2-n2dstd64-u-boot kernel: WARNING: CPU: 58 PID: 3002 at kernel/dma/direct.c:35 report_addr+0x37/0x60

    I have this code test on this instance by removing /var/log/syslog to
    force it to use journalctl output and it's failing as expected:

      Running 'journalctl -k > /tmp/journalctl-syslog'
      Checking error message in /tmp/journalctl-syslog:
      Scanning for pattern "kernel:( \[ *\d+\.\d+\])? BUG:.*"
      PASSED, log clean.
      Scanning for pattern "kernel:( \[ *\d+\.\d+\])? Oops:.*"
      PASSED, log clean.
      Scanning for pattern "kernel:( \[ *\d+\.\d+\])? kernel BUG at.*"
      PASSED, log clean.
      Scanning for pattern "kernel:( \[ *\d+\.\d+\])? WARNING:.*"
      Pattern found. Matching lines as follows:
      kernel: WARNING: CPU: 58 PID: 3002 at kernel/dma/direct.c:35 report_addr+0x37/0x60

Applied and pushed, thanks!