Make installed_version work for wheel

by using `pkg_resources.get_distribution` instead of calling pkg_info
method. Wheels don't have a .pip-egg-info folder.

See: GH-2202
Add test_installed_version_not_installed

Checks what happens when user tries to get `installed_version` property
for a InstallRequirement object when that distribution is not installed.
Merge pull request #2206 from msabramo/make_installed_version_work_with_wheel

Make installed_version work for wheel