Ignore .gitmodules file by default in HardTabs hook

This file is automatically generated by `git` and can contain hard tabs.
Ignore them by default.

Change-Id: If8abfb267cd2792f860cf9fd8abb0eeab26859c5
Reviewed-on: http://gerrit.causes.com/40327
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Silence warnings for removing empty directories

When running `git reset --hard`, `git` would sometimes display a warning
about being unable to remove a directory that wasn't empty.

This usually occurred when removing submodules. Since we don't need to
worry about this case, silence the error message by swallowing standard
error.

Change-Id: Ia7e3c0eab79e5abbe2483641124e1fe2e5cd762f
Reviewed-on: http://gerrit.causes.com/40328
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>