hook: Use core.hooksPath as hook path if set
hook: Use core.hooksPath as hook path if set

core.hooksPath can be used to configure the path to store hooks. If it
is set we should use it instead of $REPO/.git/hooks.

Signed-off-by: Fam Zheng <df9fd617995bad07eac70e27aa3fe5069270e3bd@redhat.com>

stefanha/git-publish,stefanha/git-publish