Avoid incorrect config errors on export with many --source

[theotherjimmy]

This bug was found on the website, is already going to be deployed
independent of this PR. This just upstreams the changes

[0xc0170]

/morph build

[mbed-ci]

Build : FAILURE

Build number : 1526
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6428/

[theotherjimmy]

License failure.

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1535
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6428/

Triggering tests

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

[mbed-ci]

Exporter Build : ABORTED

Build number : 1175
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6428/

[cmonr]

^^^ This should be interesting to look at tomorrow.

[studavekar]

Exporter Build : ABORTED
Build number : 1175
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6428/

gnuarmeclipse job was not completed within 2 hours and it was aborted https://mbed-os.mbedcloudtesting.com/job/exporter-build-matrix/exporter=gnuarmeclipse,target=K64F/1175/

[mbed-ci]

Test : SUCCESS

Build number : 1315
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6428/1315

[cmonr]

LGTM

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1548
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6428/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1187
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6428/

[mbed-ci]

Test : FAILURE

Build number : 1327
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6428/1327

[cmonr]

Huh. So now I'm legitimately confused. Flash cache test should not have run for NRF52 (and in this case, failed).

[cmonr]

/morph test

[mbed-ci]

Test : SUCCESS

Build number : 1332
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6428/1332