[MRG] Add better handling of invalid A-ASSOCIATE (RJ) parameters during ACSE negotiation

[scaramallion]

Reference issue

Related to #633, handle invalid result, source and diagnostic parameters in the A_ASSOCIATE string methods.

Tasks

• Unit tests added that reproduce issue or prove feature is working
• Fix or feature added
• Unit tests passing and coverage at 100% after adding fix/feature

[codecov]

Codecov Report

Merging #634 (d92c5c3) into master (21c032f) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #634   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           27        27           
  Lines         8630      8644   +14     
=========================================
+ Hits          8630      8644   +14     

Impacted Files	Coverage Δ
pynetdicom/pdu.py	100.00% <100.00%> (ø)
pynetdicom/pdu_primitives.py	100.00% <100.00%> (ø)