Add retries in case of Cobbler overloading

Offen if Cobbler run two big task in parallel
we got error based on Cobbler overloading.
If we wait and try request again, it will
process without problem. This change
implement such behavior.

Change-Id: I1e9774b9398dfb502159d7ba21e7e5b55b75b3a1
Closes-Bug: #1387699
Closes-Bug: #1396181
(cherry picked from commit 0bcc91185984a1f9e4bd68d9f247266c35349dae)