tests/qemu-iotests: re-format output to for make check-block

This attempts to clean-up the output to better match the output of the
rest of the QEMU check system when called with -makecheck. This includes:

  - formatting as "  TEST    iotest-FMT: nnn"
  - only dumping config on failure (when -makecheck enabled)

The non-make check output has been cleaned up as well:

  - line re-displayed (\r) at the end
  - fancy colours for pass/fail/skip
  - timestamps always printed (option removed)

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20190503143904.31211-1-alex.bennee@linaro.org>
Tested-by: Thomas Huth <thuth@redhat.com>