kernel-lt needs to conflict correctly with kernel in CentOS

[Andrew Woodward]

kernel-lt-* packages don't conflict distro default packages correctly leading to crummy workarounds like https://review.openstack.org/#/c/76089/

[Matthew Mosesohn (raytrac3r)]

Just some more ideas:
1 - The cleanest way to solve this is obsoletes. It will refuse to install kernel package if there's a package in an enabled repo that claims to obsolete kernel package (kernel-lt). The bad part is we can't install old kernel this way. The only way to make this part work is if we create a kernel-lt repo that is enabled only for those installs which need it. It's really a matter of adding about 8 lines to kickstart and maybe 6 lines to ISO creation process, but for many, that may seem really complex.
2 - Conflict flag will prevent both kernels from installing at the same time at package name level. Both packages can be installed from the same repo, just not at the same time. To install kernel-lt from Anaconda, the %packages section just needs these lines:
-kernel
kernel-lt

If it fails, it's because of @base or @core group issues. We may need to create a @base-lt or @core-lt package group to overcome this.

[Roman Vyalov (r0mikiam)]

we rebuilt kernel-lt-firmware in https://bugs.launchpad.net/fuel/+bug/1323354
other packages do not conflict