Xcode plugin doesn't populate any variable passed through shell (just above it).
The Variables are passed using export. But in the xcode plugin they remain unchanged.
Example: /Users/haps/Downloads/${EMBED}
OR: PROVISIONING_PROFILE=${PROVISIONING_PROFILE}

The first one of from "Embedded Profile" field and later from "Custom xcodebuild arguments"

Also JENKINS-14375 says that this issue was solved in xcode version 1.3.1, but somehow seems to be reappeared in newer one.