iotests: remove 'linux' from default supported platforms

iotests: remove 'linux' from default supported platforms

verify_platform will check an explicit whitelist and blacklist instead.
The default will now be assumed to be allowed to run anywhere.

For tests that do not specify their platforms explicitly, this has the effect of
enabling these tests on non-linux platforms. For tests that always specified
linux explicitly, there is no change.

For Python tests on FreeBSD at least; only seven python tests fail:
045 147 149 169 194 199 211

045 and 149 appear to be misconfigurations,
147 and 194 are the AF_UNIX path too long error,
169 and 199 are bitmap migration bugs, and
211 is a bug that shows up on Linux platforms, too.

This is at least good evidence that these tests are not Linux-only. If
they aren't suitable for other platforms, they should be disabled on a
per-platform basis as appropriate.

Therefore, let's switch these on and deal with the failures.

Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20200121095205.26323-2-thuth@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>