Update DownstreamContext.groovy

'SUCCESS', 'UNSTABLE' and 'FAILURE' were wrongly mapped to 48, 49 and 50 (ascii values of '0', '1' and '2'). Now the threshold names are mapped to their actual integer value instead of their ascii value.
Fix publisher tests

Fixed test to check against integer instead of ascii values.
Adding checks for blocking threshold ordinals for the case when downstreamParameterized in step context.
Ensure that block has length zero in publisher context
Merge pull request #149 from nucl303/patch-1

Parameterized Trigger Plugin support: Fix ordinal of blocking threshold