Add hpc-mon-collector to .gitignore

It is a binary file and it should never be added to the git repository.

Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

.gitignore

@@ -121,6 +121,7 @@
 /htools/ganeti-confd
 /htools/rpc-test
 /htest/hpc-htools
+/htest/hpc-mon-collector
 /htest/test
 /htools/*.prof*
 /htools/*.stat