BIGTOP-2878 : Download task does not work for git repositories

[zenmyo]

No description provided.

[ghost]

Good catch!
Took me a while to get the full picture, and I even had to write a small test to see the truth matrix

#!/usr/bin/env groovy

def final BOOLS = [false, true]
for (DOWNLOAD_URL in BOOLS)
  for (GIT_REPO in BOOLS)
    for (GIT_REF in BOOLS) {
      println("$DOWNLOAD_URL $GIT_REPO $GIT_REF")
      println ("\t\t ${(!DOWNLOAD_URL && !(GIT_REPO && GIT_REF)).toString().toUpperCase()}")
    }

but everything worked out just fine.
+1 will commit it shortly