Check libvirt version earlier

Running libvirt 0.8 causes an exception to be thrown before
has_min_version() is run, resulting in no error message about version
being logged.  This change moves the version check before the libvirt
calls are made.

Change-Id: Ifaae18c6686d72fb79fc32081c4087084ae8bbb9
Fixes: bug #1190232
Merge "Check libvirt version earlier"