Refactor: tools: Best practices for crm_shadow.c:shadow_setup()

Remove redundant name argument (was always options.instance), use bool
instead of gboolean, check CIB_shadow variable in addition to prompt,
improve messages, avoid strstr() for detecting bash shell, add doxygen,
use case-sensitive comparison for prompt.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>