network: try to eliminate default network conflict during package install
Sometimes libvirt is installed on a host that is already using the network 192.168.122.0/24. If the libvirt-daemon-config-network package is installed, this creates a conflict, since that package has been hard-coded to create a virtual network that also uses 192.168.122.0/24. In the past libvirt has attempted to warn of / remediate this situation by checking for conflicting routes when the network is started, but it turns out that isn't always useful (for example in the case that the *other* interface/network creating the conflict hasn't yet been started at the time libvirtd start its own networks). This patch attempts to catch the problem earlier - at install time. During the %post install script for libvirt-daemon-config-network, we use a case statement to look through the output of "ip route show" for a route that exactly matches 192.168.122.0/24, and if found we search for a similar route that *doesn't* match (e.g. 192.168.124.0/24) (note that the search starts with "124" instead of 123 because of reports of people already modifying their L1 host's network to 192.168.123.0/24 in an attempt to solve exactly the problem we are also trying to solve). When we find an available route, we just replace all occurrences of "122" in the default.xml that is being created with the newly found 192.168 subnet. This could obviously be made more complicated - examine the template defaul.xml to automatically determine the existing network address and mask rather than hard coding it in the specfile, etc, but this scripting is simpler and gets the job done as long as we continue to use 192.168.122.0/24 in the template. (If anyone with mad bash skillz wants to suggest something to do that, by all means please do). This is intended to at least "further reduce" occurrence of the problems detailed in: https://bugzilla.redhat.com/show_bug.cgi?id=811967
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