Why:
In case when name contains package name with exact version specified (e.g. rpm-build-4.11.3)
```
rpm -q --whatprovides "$pkg_name"
```
will tell you that no package could provide you with 'rpm-build-4.11.3',
because it's not virtual or file-provide, but exact package name.
This will lead to the installation of the package which was already installed.
It slows down manifest execution a lot.
My change will keep previous behaviour which relies on --whatprovides and
will fix wrong behaviour when argument is full package name with version.
b3a4152e00