Make pki_check.sh into an installed & supported tool

Make pki_check.sh into an installed & supported tool

* docs/pki_check.sh: Move to tool/virt-pki-validate.in and add
  in POD man page documentation
* tools/.gitignore: Ignore generated virt-pki-validate file
* tools/Makefile.am: Install & build virt-pki-validate and
  virt-pki-validate.1
* docs/remote.html, docs/remote.html.in: Refer to new tool
  name virt-pki-validate
* libvirt.spec.in, mingw32-libvirt.spec.in: Add virt-pki-validate
  and virt-pki-validate.1 to files list