Modified Makefile's clean command to actually remove "image/servicebroker"

[SamiSousa]

Found an apparent bug when running the "make clean" command, where the binary stored in "image/" isn't removed on cleanup.

[SamiSousa]

Added the line in question, restoring the previous command.

[pmorie]

@SamiSousa this is a large amount of commits for the addition of a single line.

I suggest this:

$ git reset upstream/master
$ git commit -am "Make 'make clean' remove image/servicebroker"

and then re-push to this branch.

[SamiSousa]

Thanks Paul! Learning a git command a day keeps the merge conflicts away.