[CS] findcontainer should only match exact names

The container names you give to findcontainer must be the full name of
the image, or the last part of the image name. Now, e.g., "ballot-scout"
will match `quay.io/democracyworks/ballot-scout` or `ballot-scout`, but
not `ballot-scout-webapp`.
Merge pull request #1 from turbovote/improved-findcontainer

[CS] findcontainer should only match exact names