maint: avoid static zero init in tests

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>