Switch qubes.UpdatesProxy to socat

- there are many netcat versions (openbsd, nmap, ...), which behave
 differently - especially while handling EOF
 - Debian jessie doesn't have nmap-ncat (which handle EOFs sufficiently
   good)

QubesOS/qubes-issues#1854

debian/control

@@ -116,8 +116,8 @@ Depends:
     iptables,
     net-tools,
     ethtool,
+    socat,
     tinyproxy,
-    nmap-ncat,
     ${python:Depends},
     ${misc:Depends}
 Recommends:

qubes-rpc/qubes.UpdatesProxy

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec nc localhost 8082
+exec socat STDIO TCP:localhost:8082

rpm_spec/core-agent.spec

@@ -214,7 +214,7 @@ Summary:    Networking support for Qubes VM
 Requires:   ethtool
 Requires:   net-tools
 Requires:   nftables
-Requires:   nmap-ncat
+Requires:   socat
 Requires:   qubes-core-agent
 Requires:   tinyproxy
 Conflicts:  qubes-core-vm < 4.0.0