ELBv2: fix parity in describe_target_group

[macnev2013]

Motivation

This PR fixes minor parity gaps with aws in describe_target_groups api

Fixed

• sorting the list of target group before returning it
• multiple arguments in describe call raises an exception

Added

• Added test cases for describe_target_groups api

[codecov]

Codecov Report

Merging #6812 (2216c4a) into master (c1a6609) will decrease coverage by 0.01%.
Report is 3 commits behind head on master.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master    #6812      +/-   ##
==========================================
- Coverage   96.20%   96.20%   -0.01%     
==========================================
  Files         816      816              
  Lines       80009    80022      +13     
==========================================
+ Hits        76973    76984      +11     
- Misses       3036     3038       +2     

Flag	Coverage Δ
servertests	37.01% <11.11%> (-0.01%)	⬇️
unittests	96.14% <77.77%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
moto/elbv2/responses.py	99.44% <ø> (ø)
moto/elbv2/models.py	92.65% <75.00%> (-0.12%)	⬇️
moto/elbv2/exceptions.py	90.00% <100.00%> (ø)

[bblommers]

LGTM!