Set SO_REUSEADDR when determining socket availability

The old perl DS code for detection didn't set this so was often confused
about port availability. We had to match their behavior so the installation
didn't blow up. They fixed this a while ago, this catches us up.

ipaserver/install/installutils.py

@@ -183,6 +183,7 @@ def port_available(port):
 
     try:
         s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
         fcntl.fcntl(s, fcntl.F_SETFD, fcntl.FD_CLOEXEC)
         s.bind(('', port))
         s.close()
@@ -193,6 +194,7 @@ def port_available(port):
     if rv:
         try:
             s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
+            s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
             fcntl.fcntl(s, fcntl.F_SETFD, fcntl.FD_CLOEXEC)
             s.bind(('', port))
             s.close()