AMBARI-25478. Badly formatted request may cause Ambari to crash.

[dvitiiuk]

What changes were proposed in this pull request?

Now server uses last timestamp from current metric in the case end time of range is not set.

How was this patch tested?

Manual test.

[swagle]

This is ready to merged, @hapylestat are we releasing from branch-2.7?

[hapylestat]

@swagle yes, we can merge it to 2.7