CDAP-812: Feature/startandwait service

https://issues.cask.co/browse/CDAP-812

In cdap-client, retry if we see 503 response upto a fixed limit.
It's better to check for all failure cases first:

```java
if (...) {
  throw ..
}
if (...) {
  throw ..
}
if (unavailable) {
  currentTry++;
  continue;
}
return response;
```