virusbmock: Switch to VIR_MOCK_REAL_INIT()

virusbmock: Switch to VIR_MOCK_REAL_INIT()

Since virusbmock was written 10 years ago, back when we didn't
have virmock.h and its helpers, it open codes symbol resolution
(VIR_MOCK_REAL_INIT). With a bit of cleanup (e.g. renaming
realopen to real_open and so on) it can use virmock.h provided
macros.

And while at it, drop include of virusb.h - there is no
compelling reason for it include the file. The mock just
redirects paths passed to open()/opendir().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>