Fix shell check errors & enforce it in CI

- CI already has infrastructure to enfore shell check errors
but it was not leveraged as the repo does not have a .shellcheck
file.

Fix shell check errors & enforce it in CI

- CI already has infrastructure to enfore shell check errors
but it was not leveraged as the repo does not have a .shellcheck
file.

- CI always throws the below warning in every CI

In bootstrap.sh line 11:
find -name "$file" | xargs -r rm -rf
^----------------^ SC2038: Use -print0/-0 or -exec + to allow for non-alphanumeric filenames.
^--^ SC2185: Some finds don't have a default path. Specify '.' explicitly.

In bootstrap.sh line 18:
echo 'Run "./configure ${CONFIGURE_FLAGS} && make"'
-- SC2016: Expressions don't expand in single quotes, use double quotes for that.

- Fixed SC2185,SC2038 and supressed SC2016 shell check errors.
more information regarding this errors are found at
https://github.com/koalaman/shellcheck/wiki/

TestedBy:
https://www.shellcheck.net/

Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
Change-Id: I1323741fc8ea344b6ea4e7cdf2c1b87bb8611523

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