[master] 49712a5 vmods running vmodtool require python, so check for it

[Poul-Henning Kamp]

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The fact that *building* a VMOD requires python is not a good reason
to make the Varnish *run-time* package depend on python.

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Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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