travis-tests: install less packages

asciidoc pulls in a lot of dependencies, most of those are not
needed as we just use it to convert txt to a man page. Adding
--no-install-recommended option to apt-get makes it skip those
additional dependencies. The only needed package is xmlto, so
let's add it explicitly.

This results is some 50 packages being skipped (mostly TeX/LaTeX and
some extra SGML tools), wow!
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

scripts/travis/travis-tests

@@ -4,7 +4,7 @@ set -x -e
 TRAVIS_PKGS="protobuf-c-compiler libprotobuf-c0-dev libaio-dev
 		libprotobuf-dev protobuf-compiler python-ipaddr libcap-dev
 		libnl-3-dev gcc-multilib libc6-dev-i386 gdb bash python-protobuf
-		libnet-dev util-linux asciidoc"
+		libnet-dev util-linux asciidoc xmlto"
 
 travis_prep () {
 	[ -n "$SKIP_TRAVIS_PREP" ] && return
@@ -31,7 +31,7 @@ travis_prep () {
 	fi
 
 	apt-get update -qq
-	apt-get install -qq $TRAVIS_PKGS
+	apt-get install -qq --no-install-recommends $TRAVIS_PKGS
 	chmod a+x $HOME
 }