devtest_uc: Don't print the pid in the error msg

Updates our missing TE_DATAFILE error message so we print $1
instead of the PID of our bash process.

Previously you would get an error message like:

 "A test environment description is required as 1234."

Change-Id: Ib669951e0a5e980075ea09caeebdaab9f67bf83a
Merge "devtest_uc: Don't print the pid in the error msg"