bootstrap: fix shellcheck warnings

Shellcheck reports issues in the [mostly] common bootstrap
script found in our autotools repositories.  Apply fixes
for the issues reported by this tool:

- not handling filenames with spaces.
- not using portable `find` parameters.
- squash warning for purposeful string non-evaluation in
  help-text.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I86ef079c9632e5563a1a56d6a2e23aad59ecbc57
1 file changed