Expand Hashicorp acceptance tests

[chris-j-h]

• Add tests for Hashicorp TLS and authentication methods
• Sample certificates and keystores have been added for use in acceptance tests
• Re-enable JDK 11 Travis build

[codecov-io]

Codecov Report

Merging #605 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #605      +/-   ##
============================================
+ Coverage     99.46%   99.46%   +<.01%     
  Complexity     1709     1709              
============================================
  Files           264      264              
  Lines          5216     5218       +2     
  Branches        252      252              
============================================
+ Hits           5188     5190       +2     
  Misses            5        5              
  Partials         23       23

Impacted Files	Coverage Δ	Complexity Δ
.../key/vault/hashicorp/HashicorpKeyVaultService.java	100% <100%> (ø)	8 <0> (ø)	⬇️

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