Always write the template in order to make it easier to debug isolation mode

[dawehner]

Debugging the isolation mode can be tricky as xdebug doesn't help you
with the initial $job piped into the php process.

As solution this PR uses the same technique as the windows util,
which is dumping the template into a temporary file and include it from there.

[sebastianbergmann]

I think #1342 is the better solution.

[dawehner]

@sebastianbergmann
This is an additional / orthogonal issue. #1342 won't solve the problem how we deal with the actual executed PHP code, though I'm happy to work on #1342, actually have a local branch for that already