gitignore: Ignore new generated man page

Commit 3762a03added3 added vdsm-tool manual, but did not upadte
.gitignore, which broke "make check".

Change-Id: I065c41326f40b46aff6069d9664a50467e83afa3
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28419
Reviewed-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>