Fix traceback when running mbed test

[bridadan]

Description

This should fix #8619.

The issue came down to the use of the Python function map() and that being present in a data structure that is serialized to json. Turns out, you can't serialize the output of map()! (Hence the error). This wraps the call to map in list() to force it to be serializable.

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3655
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8782/

Triggering tests

/morph test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 3262
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8782/

[mbed-ci]

Test : SUCCESS

Build number : 3435
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8782/3435