catch mapping exception for old jenkins jobs

log the error with println because the debug trait is not visible here...
random delay to avoid confusing github

hypothesis: github is confused by commit statuses with the same timestamp
solution: add random delay before setting status

review by @dragos
normalizeSha
normalize shas in checker and commenter

not the ideal solution, but will have to do for now
some more hacky robustness for jenkins api

buildStatusForJob now returns an empty stream if something goes wrong
Jenkins api accepts parameters without values

The Jenkins api now accepts jobs with parameters that only specify their name,
not their value. Scala's PR validation jobs also take a password parameter.
Merge pull request #33 from adriaanm/master

deal with old-style jenkins jobs, randomize timing for commit status, normalize shas