Add tightvncserver as the default vncserver on JCK pLinux machines

[sxa]

Seems the vnc4server that is installed on the JCK Linux/PPCLE machines has an issue when you connect to it. tightvncserver works ok (So effectively this is the opposite to what we need on zLinux - Ref #424 ) We should ensure that vnc4server is removed and tightvncserver installed and is the default vncserver on the systems in order to reduce confusion for those running the tests and to keep the manual test documentation as simple as possible.

Thu Aug  9 14:55:11 2018
 Connections: accepted: 127.0.0.1::52168
 SConnection: Client needs protocol version 3.7
 SConnection: Client requests security type VncAuth(2)

Thu Aug  9 14:55:14 2018
 VNCSConnST:  Server default pixel format depth 16 (16bpp) big-endian rgb565

Thu Aug  9 14:55:15 2018
 VNCSConnST:  Client pixel format depth 8 (8bpp) rgb max 3,3,3 shift 4,2,0
 Connections: closed: 127.0.0.1::52168 (Internal error: inPF is not native
              endian)
 SMsgWriter:  framebuffer updates 0
 SMsgWriter:    raw bytes equivalent 0, compression ratio nan