tests: Fix most of errors reported by shellcheck

BUG=none
BRANCH=none
TEST=make runtests

Signed-off-by: Jakub Czapiga <czapiga@google.com>
Change-Id: I364ac6ace35705f1cfdaec71297523d4c2132b75
Disallow-Recycled-Builds: test-failures
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3695417
Reviewed-by: Julius Werner <jwerner@chromium.org>
32 files changed