Add testing-setup.sh script to enable dev test mode

This script, kept under a dev/ folder, will set dash as a shell
(configurable at runtime) and reduce key sizes to 512-bit. These make
testing more efficient during code development.
Auto-detect vars when present and allow configless use

To avoid the need to explicitly source the vars configuration, the file
location is auto-detected at runtime. This is skipped when the $EASY_RSA
path is defined (non-zero) or when $EASY_RSA_EXPERT is defined.

The autodetect vars search order is: cwd, then program path.
Remove embedded newline escapes for shell compat

Bash (and possibly other shells) require an explicit -e argument to echo
to support this. This interferes with other shells, so all \n sequences
are now removed.