expect-post-runner.sh: Disable backtracing

This script sources utils.sh, which automatically enables shell backtracing
support on any error (i.e. subcommand exiting with non-0 status). But
expect-post-runner.sh handles exit codes itself, and not intended to terminate
on first non-0 code, so disable "ERR" trap, used for backtracing.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I5ae9959914af4573d8aede47ac8cc93106733759
diff --git a/script/expect-post-runner.sh b/script/expect-post-runner.sh
index 3b38e65..92fff75 100755
--- a/script/expect-post-runner.sh
+++ b/script/expect-post-runner.sh
@@ -12,6 +12,10 @@
 ci_root="$(readlink -f "$(dirname "$0")/..")" && \
     . "${ci_root}/utils.sh"
 
+# utils.sh automatically enablea fail-fast backtracing, but we don't to fail
+# on first non-zero exit code, we handle them ourselves here.
+trap - ERR
+
 archive="${WORKSPACE}/artefacts-lava"
 
 # Extract UART numbering from the FVP common log using the ports script