Store kvm dirty bitmap inside firecrackers internal bitmap so no data is
lost incase of an error

Signed-off-by: Jack Thomson <jackabt@amazon.com>
Co-authored-by: Roman Kovtyukh <HelloDearGrandma@gmail.com>
Co-authored-by: Pablo Barbáchano <pablob@amazon.com>

Only if the snapshot writing fails then store the kvm buffer inside the
firecracker internal bitmap. Also attempted to make the filling
algorithm in the test to be dynamic so it will work on ARM
chips

Signed-off-by: Jack Thomson <jackabt@amazon.com>