Fixing memory leaks in add-context command

Besides enforcing the return values and outputting --help to stdout, the
problem lay with the instances of struct ctx_type *type being created
but not assigned to the doubly-linked list under various error
conditions.

Signed-off-by: Daniel U. Thibault <daniel.thibault@drdc-rddc.gc.ca>
Signed-off-by: David Goulet <dgoulet@efficios.com>