fixes ovirt 3.1 related issue.

This patch includes 5 fixes:
1. Test connection was not working in Compute resource Edit page.
2. oVirt 3.1 does not include Blank template in each virtual data center, as a workaround I have included an empty template in foreman template selector.
3. oVirt 3.1 fixes limitation of earlier versions, it allows creating number of disks for a single VM in the same time, now foreman can take advantage of this fix.
4. Fix foreman issue #2224 by bumping rbovirt version to version 0.0.18 that include a fix.
5. Fix foreman issue #2163 by including fog git version that contains the fix.