fix(script): enforce gawk to be installed

If gawk is not installed, a weird error is encountered as shown
below when make_stress_test_image.sh script is executed locally:

losetup: failed to parse size: '5.24078e+09': Invalid argument

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: Ibe3b212516e2cc036f1503f61786c146ea885b78
1 file changed