Fail if any of the install-exec-hook commands fails.

Hopefully, this will mean that somebody doing a set-UID/set-GID/setcap
installation as themselves rather than as root will not "succeed" but
leave dumpcap installed without enhanced privileges, so the underlying
problem in bugs such as bug 10247 will be more obvious.

Change-Id: I34393bc2c9ea4dc59854a08524edb4f65e79730b
Reviewed-on: https://code.wireshark.org/review/2781
Reviewed-by: Guy Harris <guy@alum.mit.edu>