tests: fix dezip of ubuntu images in long regr
tests: fix dezip of ubuntu images in long regr

needed to change output open from 'w' to 'wb'
to write binary format

Change-Id: Ia176d86a8ab8cc083ffc9508e051b667936eca2c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36615
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Reviewed-by: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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