add gCTS polling on timeouts

[jfilak]

GET /repository//getHistory
{ result: [ { rid: , checkoutTime: , fromCommit: , toCommit: , caller: , request: , type: (PULL | CLONE), state: DONE, rc: } ] }

[palubaj]

Check out polling already implemented for the clone operation (see #103).

Basically, the clone operation is executed, and if it fails, raising 500 Internal Error, the return code of the operation is checked. The reason to check the return code is that, in some cases, even though the operation raises an error, it was successful (the raised error was a response from a server). To get the return code, the getHistory endpoint is used.