Icetea/Greetea: TypeError: a bytes-like object is required, not 'str'

[MarceloSalazar]

Description

During OOB for 5.10 release, found issues while evaluating icetea:

• Mbed CLI 1.8.2
• Mbed OS 5.10 rc3
• OSX El Capitan
• Python 3.7

git clone https://github.com/ARMmbed/mbed-os
cd mbed-os
git checkout mbed-os-5.10.0-rc3
mbed test -m K64F -t GCC_ARM --compile --icetea -vv
...
[mbed-85384] Exec "/usr/local/opt/python/bin/python3.7 -u /Users/marsal01/mbed/OOB/5.10-rc3-2/mbed-os/tools/run_icetea.py -m K64F -t GCC_ARM -v --application-list" in "/Users/marsal01/mbed/OOB/5.10-rc3-2/mbed-os"
Traceback (most recent call last):
  File "/Users/marsal01/Library/Python/3.7/lib/python/site-packages/mbed/mbed.py", line 3338, in main
    status = pargs.command(pargs)
  File "/Users/marsal01/Library/Python/3.7/lib/python/site-packages/mbed/mbed.py", line 1985, in thunk
    return command(**argv)
  File "/Users/marsal01/Library/Python/3.7/lib/python/site-packages/mbed/mbed.py", line 2878, in test_
    if applications_to_add and 'TEST_APPS-' in applications_to_add:
TypeError: a bytes-like object is required, not 'str'
[mbed-85384] ERROR: Unknown Error: a bytes-like object is required, not 'str'
---

Issue request type

[ ] Question
[ ] Enhancement
[X] Bug

@OPpuolitaival @cmonr @jamesbeyond

Note: this also happens when running greentea:

mbed test -m K64F -t GCC_ARM --compile -vv

Not a problem with Python 2.

[jamesbeyond]

I can reproduce on Ubuntu 16.04 with Python 3.7. Both with IceTea and GreenTea.
IceTea throws the error right away.
GreenTea throws the error in the end.

But the IceTea error is from mbed-cli mbed.py and GreenTea error is from mbed-os build_api.py

[ciarmcom]

ARM Internal Ref: MBOTRIAGE-1703

[0xc0170]

@OPpuolitaival

[OPpuolitaival]

Fix: #8181

[0xc0170]

Fixed via 8181