Fixes #340

Problem resolution :

1. Catch the exception
2. Log the exception :
   □ Log level: warning
   □ Message: "Login failure: " + details

Testing :

1. Three tests

• Test 1 :
  Two clouds are configured and both are available
  Two jobs
  Expected result: Both jobs are built

• Test 2 :
  First Cloud down - simulate outage by providing invalid credentials
  Two jobs
  Expected result: Both jobs should be built using the remaining cloud

• Test 3 :
  Second Cloud down - simulate outage by providing invalid credentials
  Two jobs
  Expected result: Both jobs should be built using the remaining cloud

2. Adjustments
   □ Made The LoginFailure exception (From JCloudsCloud.java) public so it can be used during the tests
   □ Added (overloaded ) a MockJCloudsCloud constructor to provide clouds with null credentials for the tests

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