Fix find-value-in-files to return an empty string if no values found

[sfloess]

Using find-value-in-files to locate test classes (or triggers) will yield a space when nothing is found. This is ugly later when deciding about running tests and computing how we build the runTask stanza (per #211). The following is what can be seen on the console to illustrate:

• Test Classes: [TaskUtils_Test ]
• Test Classes: [ ]

[sfloess]

@pcon,

Will you be so kind as to test the fix in branch sfloess_issue-211? I've got a fix out and believe this works... I tested with both no changes to classes and a lone test class change. Fairly certain this is the correct fix.

Upon your ack, I will merge to master.

Thanks - and sorry this one took so long to resolve!