iotests: explicitly pass source/build dir to 'check' command

iotests: explicitly pass source/build dir to 'check' command

The 'check' script has some rather dubious logic whereby it assumes
that if invoked as a symlink, then it is running from a separate
source tree and build tree, otherwise it assumes the current working
directory is a combined source and build tree.

This doesn't work if you want to invoke the 'check' script using
its full source tree path while still using a split source and build
tree layout. This would be a typical situation with meson if you ask
it to find the 'check' script path using files('check').

Rather than trying to make the logic more magical, add support for
explicitly passing the dirs using --source-dir and --build-dir. If
either is omitted the current logic is maintained.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Acked-by: Hanna Czenczek <hreitz@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230303160727.3977246-2-berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230315174331.2959-19-alex.bennee@linaro.org>