libexport.a: Allow client_init() to fail instead of exit

client_init()'s current callers can now deal correctly with a failure.
Get rid of code that can cause our process to exit in client_init(),
if address mask parsing or memory allocation fails.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>