maint: avoid static zero init in tests
    
    C guarantees that static variables are zero-initialized.  Some older
    compilers (and also gcc -fno-zero-initialized-in-bss) create larger
    binaries if you explicitly zero-initialize a static variable.
    
    * tests/eventtest.c: Fix initialization.
    * tests/testutils.c: Likewise.
    * tests/virhostdevtest.c: Likewise.
    * tests/virportallocatortest.c: Likewise.
    * tests/virscsitest.c: Likewise.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>