SimpleFillOS: add unit tests for OS parameter merging
SimpleFillOS: add unit tests for OS parameter merging

Adds tests to ensure OS parameters are dealt with consistently.

Signed-off-by: Santi Raffa <6a214b96de92f36f05379f829a80c82d50682e4c@google.com>
Reviewed-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>

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