selftests/mount: Make git ignore all binaries in mount test suite

This patch includes the mount test binaries into the .gitignore
file listing in their respective directories. This will make sure
that git ignores all of these test binaries when displaying status.
Signed-off-by: Zhang Zhen <zhenzhang.zhang@huawei.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/mount/.gitignore

+unprivileged-remount-test