fix all shellcheck warnings

[marc-hb]

shellcheck finds bugs, notably issues with set -e: do this before

• [sof-test] add set -e to all test cases (Unless You Love Debugging) #312

Related:

• clean-up: move all shell script code to a function and use a "main" #740

[greg-intel]

Current status..

Not many issues left with files that are used across-the-board.

[greg-intel]

Another Update

[greg-intel]

There are currently seven open PRs, once they're all merged I believe this ticket can be closed, @marc-hb ?