Change loopback key "test_peripheral" to "test_peripheral_name"

The key for an int field was being used with a String.
This was causing the JSON file to be rejected.

This was based on ag/20951548

Bug: 245751695
Bug: 296123121
Test: install CTS Verifier
Test: run loopback test
Test: save report
Test: adb pull /sdcard/verifierReports
Test: check JSON file, see b/296123121
Change-Id: Id1a0e24bd85b52db36a8c1f72f8cd3bd25d43107
Merged-In: Id1a0e24bd85b52db36a8c1f72f8cd3bd25d43107