Only ignore container-storage in root

Previously, git was ignoring the pattern 'container-storage' everywhere.
Since changes to `cmd/container-storage` may be desirable, anchor the
pattern to the repo root only.

Signed-off-by: Chris Evich <cevich@redhat.com>

.gitignore

@@ -25,8 +25,5 @@ man/man5
 man/man8
 vendor/pkg/
 .vagrant
-containers-storage
-containers-storage.darwin.amd64
-containers-storage.linux.amd64
-containers-storage.linux.386
-containers-storage.linux.arm
+/containers-storage
+/containers-storage.*