Debug QuotaWatchers creation and cleaning

[malish8632]

This change moving creation of QuotaWatcher closer to its usage minimizing chance of exceptional exit before it is used.
Wraps main call to try/catch in order to properly clean QuotaWatcher map.
It also uses QuotaWatcher as key in ConcurrentMap.

[sming]

LGTM

[codecov]

Codecov Report

Merging #702 into master will decrease coverage by 0.05%.
The diff coverage is 65.00%.

@@             Coverage Diff              @@
##             master     #702      +/-   ##
============================================
- Coverage     54.21%   54.15%   -0.06%     
+ Complexity     3040     3037       -3     
============================================
  Files           735      735              
  Lines         19809    19808       -1     
  Branches       1305     1304       -1     
============================================
- Hits          10740    10728      -12     
- Misses         8602     8614      +12     
+ Partials        467      466       -1     

Impacted Files	Coverage Δ	Complexity Δ
.../com/spotify/heroic/metric/LocalMetricManager.java	66.07% <65.00%> (-0.40%)	4.00 <0.00> (ø)
...src/main/java/com/spotify/heroic/metrics/EWMA.java	58.33% <0.00%> (-20.84%)	4.00% <0.00%> (-1.00%)
...rc/main/java/com/spotify/heroic/metrics/Meter.java	68.96% <0.00%> (-17.25%)	6.00% <0.00%> (-2.00%)

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