Add arbitrary node support to create/remove disks
Add arbitrary node support to create/remove disks

Currently the cmdlib _CreateDisks and _RemoveDisks always work on the
instance's (current/primary) nodes. This patch extends them to take an
additional target_node parameter denoting that the creation/removal
should ignore the current instance nodes and instead operate on the
given node.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>

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