add services to libzypp, ensure /etc/zypp is writabale in inst-sys
Merge pull request #11 from yast/save_credentials

Save credentials
save repositories before refreshing added services

- otherwise pkg-bindings will treat them as removed by the service refresh and
  unload them)
- 3.1.5
Merge pull request #12 from yast/save_fix

save repositories before refreshing added services
fixed mounting write copy of /etc/zypp at installation

- 3.1.6
Merge pull request #13 from yast/mount_fix

fixed mounting write copy of /etc/zypp at installation
display progress when adding registered services

- 3.1.7
Merge pull request #14 from yast/progress

display progress when adding registered services
Add SLP service discovery dialog for registration (FATE#316384)