tests/migration/i386: Speed up the i386 migration test (when using TCG)

tests/migration/i386: Speed up the i386 migration test (when using TCG)

When KVM is not available, the i386 migration test also runs in a rather
slow fashion, since the guest code takes a couple of seconds to print
the "B"s on the serial console, and the migration test has to wait for
this each time. Let's increase the frequency here, too, so that the
delays in the migration tests get smaller.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220819053802.296584-4-thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220822165608.2980552-5-alex.bennee@linaro.org>