Don't install XLT everytime a machine is started

[jowerner]

Currently, XLT is installed freshly whenever a machine is started. XLT should be installed only once when creating the image.

But note that the password that grants remote access to the agent controller may change between machine starts. So patching the current password into the agent controller configuration must be robust enough to also replace an existing value.

[rschwietzke]

How about taking the PWD from the env instead of patching it into the files?

[jowerner]

XLT needs to be extended to support that.

[h-arlt]

This approach was taken for a good reason: every time the machine starts, all residues from previous runs should be gone so that XLT runs with a clean working directory (of course, there might be other ways to do so but we decided to keep it simple). Thus, I don't see any benefit to change that without a good reason.

[h-arlt]

To avoid misunderstandings: the term installation might be confusing here as the Packer scripts refer to installation by downloading the XLT archive to the home directory of the xlt user; extracting the XLT archive into the working directory is a preparation step of the agent controller startup routine.