Fix source install

Since git install check is not works as expected, "install git from source" task does not work even if we set `git_install_from_source` to true.
I create test for it and fix the git install check problem.

test result on Travis-CI:
- Just add test: https://travis-ci.org/xKerman/ansible-role-git/builds/33409058
- Fix Git install check: https://travis-ci.org/xKerman/ansible-role-git/builds/33410262