maint: avoid static zero init in tools
    
    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.
    
    * tools/virsh-console.c (got_signal): Drop unused variable.
    * tools/virsh-domain.c: Fix initialization.
    * tools/virsh.c: Likewise.
    * tools/virt-host-validate-common.c (virHostMsgWantEscape):
    Likewise.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>