travis-ci: add 'make distcheck' to test scenario, V2

travis-ci: add 'make distcheck' to test scenario, V2

in rare cases openvpn is built from tarball, it happens during "installer
build"
process. "make distcheck" helps to prevent problems during such builds.

V2: limit "make distcheck" to one build configuration
Signed-off-by: Ilya Shipitsin <chipitsine@gmail.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1488045604-25460-1-git-send-email-chipitsine@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14208.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>