Fix race condition in parallel execution of "make install".

Fix race condition in parallel execution of "make install".

ovs-vsctl is listed, incorrectly, in both bin_PROGRAMS and bin_SCRIPTS.
This meant that "make install" with the -j option could try to install
ovs-vsctl two times in parallel, a race that occasionally caused a build
failure, e.g.:
http://buildd.debian.org/status/fetch.php?pkg=openvswitch&arch=s390&ver=1.4.2%2Bgit20120612-5&stamp=1342851603

Debian bug #682384.
CC: 682384@bugs.debian.org
Reported-by: Bastian Blank <waldi@debian.org>
Signed-off-by: Ben Pfaff <blp@nicira.com>