util: capabilities detection for dnsmasq
In order to optionally take advantage of new features in dnsmasq when the host's version of dnsmasq supports them, but still be able to run on hosts that don't support the new features, we need to be able to detect the version of dnsmasq running on the host, and possibly determine from the help output what options are in this dnsmasq. This patch implements a greatly simplified version of the capabilities code we already have for qemu. A dnsmasqCaps device can be created and populated either from running a program on disk, reading a file with the concatenated output of "dnsmasq --version; dnsmasq --help", or examining a buffer in memory that contains the concatenated output of those two commands. Simple functions to retrieve capabilities flags, the version number, and the path of the binary are also included. bridge_driver.c creates a single dnsmasqCaps object at driver startup, and disposes of it at driver shutdown. Any time it must be used, the dnsmasqCapsRefresh method is called - it checks the mtime of the binary, and re-runs the checks if the binary has changed. networkxml2argvtest.c creates 2 "artificial" dnsmasqCaps objects at startup - one "restricted" (doesn't support --bind-dynamic) and one "full" (does support --bind-dynamic). Some of the test cases use one and some the other, to make sure both code pathes are tested.
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