Shell script cleanups

Summary:

Shell script cleanups:

  - Add required space to [ -n ].
  - Avoid quote within quote.
  - Exit if cd fails.
  - Remove \n which is not handled by echo.

Backport of core PR10773
https://github.com/bitcoin/bitcoin/pull/10773/files

Note: tidy_datadir.sh, gitian-build.sh and verify_commits.sh have
been deleted from our codebase.

Depends on D3955.

Test Plan:
Run the scripts (build the project to test genbuild.sh).
I did not test the detached-sig-create.sh script which is just an
echo change, not the verify.sh which is obsolete and need rework.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D3956