Disallow setting an app to zero instances

When instances is zero strange things happen, and if you want no instances you should just stop your app!
We also changed the default so no one has to set this explicitly.

Signed-off-by: Eric Malm <emalm@pivotallabs.com>
Encrypted attribute spec handles non-exception-raising case

* Decrypting with the wrong encryption key is not guaranteed
to raise a CipherError. In the case where the decrypt succeeds,
we check that the decrypted value does not match the original plaintext.

* We intend this to fix the flakiness of this test, especially in Travis runs.

Signed-off-by: Chris Adams <cadams@pivotallabs.com>
send build artifacts upload/download uri to diego

Signed-off-by: Phan Le <ple@pivotallabs.com>
add CF_DIEGO_BETA env var to opt into diego
Checks that app file size is within limits before adding to appbitscache