Add handle to postgres DB

[avaczi]

This was somehow forgotten when first adding the cluster discovery. In the manually created entities it's there, and that results in situations where two entities of the same thing report different things (an error and the expected values, respectively).

[codecov[bot]]

Codecov Report

Merging #134 into master will increase coverage by 0.02%. The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master     #134      +/-   ##
==========================================
+ Coverage    77.3%   77.33%   +0.02%     
==========================================
  Files           6        6              
  Lines         855      856       +1     
==========================================
+ Hits          661      662       +1     
  Misses        194      194

Impacted Files	Coverage Δ
zmon_aws_agent/postgresql.py	83.45% <81.81%> (+0.12%)	:arrow_up:

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[Jan-M]

:+1:

[avaczi]

:+1:

[mohabusama]

👍

[avaczi]

:+1: