tests/qemu-iotests/check: Allow tests without groups

tests/qemu-iotests/check: Allow tests without groups

The regular expressions in the "check" script currently expect that there
is always a space after the test number in the group file, so you can't
have a test in there without a group unless the line still ends with a
space - which is quite error prone since some editors might remove spaces
at the end of lines automatically.
Thus let's fix the regular expressions so that it is also possible to
have lines with one test number only in the group file.

Suggested-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190717111947.30356-2-thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>