maint: avoid static zero init in tools

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>