Almost all invocations of run-test have either "$* on $(TARGET_NAME)"
or "$< on $(TARGET_NAME)" as the last argument.  So provide a default
test name, while allowing an escape hatch for custom names.

As an additional simplification, remove the need to do shell quoting.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220929114231.583801-24-alex.bennee@linaro.org>