block_devices -> kvm_disks renaming
block_devices -> kvm_disks renaming

and a couple more styple fixes.
block_devices are misleading so rename them to kvm_disk (just like kvm_nics)

Signed-off-by: Dimitris Aragiorgis <4514117c4a99256e19437c7e3407c4ecbf98aec0@grnet.gr>
Signed-off-by: Thomas Thrainer <98bdeac947eb8ca18146e9ce7f092788ec242cd1@google.com>
Reviewed-by: Thomas Thrainer <98bdeac947eb8ca18146e9ce7f092788ec242cd1@google.com>

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