ci: explicitly skip I/O tests on alpine

ci: explicitly skip I/O tests on alpine

The block I/O tests don't work on Alpine because their alternative libc
impl emits different strings for errnos, which breaks the expected
output matching. e.g.

=== IO: pattern 102
 wrote 512/512 bytes at offset 512
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-qemu-img: Error while reading offset 0 of blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
+qemu-img: Error while reading offset 0 of blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: I/O error
 4
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824
 Formatting 'TEST_DIR/t.IMGFMT.2', fmt=IMGFMT size=0

Currently the I/O tests are skipped as a side effect of the Alpine image
containing a minimal busybox 'sed' binary, rather than GNU sed. This is
a fragile assumption that will be invalidated when the dockerfile is
changed to be autogenerated from a standardized package list that
includes GNU sed.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20211215141949.3512719-6-berrange@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20220105135009.1584676-6-alex.bennee@linaro.org>