double up [ for safety

The construct [ "$UNSET_VAR" -eq "1" ] will throw a bash error of
'integer expression expected' if UNSET_VAR doesn't exist. In bash
we can protect this by doubling up the brackets.

Change-Id: I261212c9d225b756a82214aa28d9e43e5d89fe55
Merge "double up [ for safety"