scripts: allow to skip travis specific parts in travis-tests

We are going to use this script for testing linux-next.

v2: remove bashism
travis-ci: success for scripts: allow to skip travis specific parts in travis-tests (rev2)
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

scripts/travis/travis-tests

 #!/bin/sh
 set -x -e
 
-ulimit -c unlimited
+travis_prep () {
+	[ -n "$SKIP_TRAVIS_PREP" ] && return
+
+	cd ../../
+
+	service apport stop
 
-cd ../../
+	apt-get update -qq
+	apt-get install -qq protobuf-c-compiler libprotobuf-c0-dev libaio-dev	\
+		libprotobuf-dev protobuf-compiler python-ipaddr libcap-dev	\
+		libnl-3-dev gdb bash python-protobuf
+	chmod a+x $HOME
+}
 
-service apport stop
+travis_prep
+
+ulimit -c unlimited
 echo "|`pwd`/test/abrt.sh %P %p %s %e" > /proc/sys/kernel/core_pattern
 
-apt-get update -qq
-apt-get install -qq protobuf-c-compiler libprotobuf-c0-dev libaio-dev	\
-	libprotobuf-dev protobuf-compiler python-ipaddr libcap-dev	\
-	libnl-3-dev gdb bash python-protobuf
-chmod a+x $HOME
 export GCOV=1
 make
 make -C test/zdtm