iotests: fix leak of tmpdir in dry-run mode

iotests: fix leak of tmpdir in dry-run mode

Creating an instance of the 'TestEnv' class will create a temporary
directory. This dir is only deleted, however, in the __exit__ handler
invoked by a context manager.

In dry-run mode, we don't use the TestEnv via a context manager, so
were leaking the temporary directory. Since meson invokes 'check'
5 times on each configure run, developers /tmp was filling up with
empty temporary directories.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20240205154019.1841037-1-berrange@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit c645bac4e06bf9642cc8e339d027a5d6ec54d811)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>