Instance generators
Instance generators

This patch introduces and enhances generators for
instances:
- 'genInstWithNets' is split into the generation of an
  arbitrary instance and enhancing an instance with nets
- 'genInst' calls 'genInstWithNets' with an empty set
  of initial networks to provide a reasonable default
- the Arbitrary instance of 'Instance' uses now 'genDisks'
  to create instances with a reasonable set of disks

Signed-off-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

dimara/ganeti,yiannist/ganeti,dimara/ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,grnet/snf-ganeti,mbakke/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,yiannist/ganeti,andir/ganeti,apyrgio/snf-ganeti,apyrgio/ganeti,mbakke/ganeti,grnet/snf-ganeti,onponomarev/ganeti,yiannist/ganeti,leshchevds/ganeti,bitemyapp/ganeti,andir/ganeti,leshchevds/ganeti,andir/ganeti,leshchevds/ganeti,apyrgio/ganeti,ganeti/ganeti,bitemyapp/ganeti,mbakke/ganeti