Try to fix occasionally failing integration test.

[Patrik-Stas]

The test test_create_credential_works_twice occasionally fails in CI - never run into this issue locally. The CI failure of this test is such that the second of creating the same credential definition passes, while it's expected to fail. I think the reason is that probably on the second attempt, the created credential definition is not yet fully propagated through the pool, and so it appears like the credential definition doesn't exist yet.
This PR add timeout into the test between first and second attempt to create the same cred. definition.

Signed-off-by: Patrik Stas patrik.stas@absa.africa

[codecov-commenter]

Codecov Report

Merging #310 (9498698) into master (42e8038) will decrease coverage by 4.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #310      +/-   ##
==========================================
- Coverage   49.72%   45.55%   -4.18%     
==========================================
  Files         155      153       -2     
  Lines       19639    18783     -856     
  Branches     6202     5888     -314     
==========================================
- Hits         9766     8556    -1210     
- Misses       5072     6114    +1042     
+ Partials     4801     4113     -688     

Flag	Coverage Δ
integration	?
unittests	45.55% <ø> (ø)

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

Impacted Files	Coverage Δ
libvcx/src/credential_def.rs	36.47% <ø> (-11.87%)	⬇️
libvcx/src/libindy/utils/pool.rs	14.58% <0.00%> (-52.42%)	⬇️
libvcx/src/libindy/utils/anoncreds.rs	17.81% <0.00%> (-47.02%)	⬇️
libvcx/src/utils/plugins.rs	0.00% <0.00%> (-33.34%)	⬇️
libvcx/src/libindy/utils/ledger.rs	12.00% <0.00%> (-27.24%)	⬇️
libvcx/src/utils/random.rs	75.00% <0.00%> (-25.00%)	⬇️
libvcx/src/utils/devsetup.rs	41.63% <0.00%> (-21.04%)	⬇️
libvcx/src/init.rs	25.80% <0.00%> (-20.97%)	⬇️
libvcx/src/utils/devsetup_agent.rs	0.00% <0.00%> (-20.33%)	⬇️
libvcx/src/libindy/utils/payments.rs	38.88% <0.00%> (-13.20%)	⬇️
... and 27 more

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