support for new major version of sysrepo 1.4

Our code uses the last old version 0.7.8. The sysrepo project has a new major version - 1.4.2 2.0. They say it's almost complete rewrite with some major changes. For details see:

https://github.com/sysrepo/sysrepo#migration-from-sysrepo-version-07x-or-older

UPDATE(Tomek): After initial investigation, it seems that migrating to 2.0 is too risky, for the following reasons:

• there are no C++ bindings available yet that we depend on heavily
• the future of the C++ bindings is uncertain. There is one person on github that is supposed to work on it, but there is no visible progress on this. In any case, it will appear in a separate repo
• there are no packages available for major distros.

Considering the above, we decided to upgrade to sysrepo 1.4.