tpm2_sessionconfig fix usage of --disable-continuesession (5.6.X)

[JuergenReppSIT]

• The test with the tss master is now running on ubuntu 20.04 instead of 18.04
• If continue session was disabled a error did occur in the function for restoring the session context. Now after usage of an session with continue session disabled the context will not be saved and the session context file will be deleted. In one integration test continue session is now disabled and the flush for this session is removed.

[codecov[bot]]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (a36f8e2) 76.52% compared to head (7247d7a) 76.52%.

Files	Patch %	Lines
lib/tpm2_session.c	61.90%	8 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##            5.6.X    #3349   +/-   ##
=======================================
  Coverage   76.52%   76.52%           
=======================================
  Files         173      173           
  Lines       23648    23663   +15     
=======================================
+ Hits        18096    18108   +12     
- Misses       5552     5555    +3     

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