The upload-swift-artifacts script needs to handle json encoding of
the Temp-Url-Key property, and [1] was a step in the right direction.
However, it contained two errors that this patch corrects:
1. The property name is "Temp-Url-Key" (camel-case). Even if you specify
"Temp-URL-Key" something will change "URL" to "Url". This patch uses
the correct form when detecting whether the property exists.
2. The logic for detecting whether the Temp-Url-Key property exists was
inverted. The property doesn't exist when the jq output is "null".
[1] Ife347f754ca9129580c092bb271bacdc032ae14b
Change-Id: Idf0dccf4cd7d040e803b2ed2b49b3c39919c5a60
29367cb96d