Properly handle template branch names that contain a forward slash

[foosel]

If the templateBranchName is a branch containing a forward slash (e.g. dev/v1.0) this leads to errors when trying to retrieve the job's config from Jenkins (since Jenkins interprets the / as part of the URL and therefore throws a 404). This PR runs the templateBranchName through the same conversion (/ -> _) as the job names created from git branches. Thus, for a templateBranchName like the above example, the expected name of the template job is dev_v1.0, matching the general pattern the script expects.

[michaelglass]

fyi: workaround is to have origin/branch_name as the branch name in your template project (for us, we use origin/master)

[kschzt]

+1 - thank you, this works (workaround did not)