Component SD test: skip multiple thread test depending on RAM

[jeromecoutant]

Description

Got issue with this test:
components-storage-blockdevice-component_sd-tests-filesystem-parallel
with few NUCLEO boards.

[1539050335.92][CONN][RXD] >>> Running case #2: 'Filesystem access from multiple threads'...
[1539050336.03][CONN][RXD] ++ MbedOS Error Info ++
[1539050336.08][CONN][RXD] Error Status: 0x8001011F Code: 287 Module: 1
[1539050336.12][CONN][RXD] Error Message: Operator new[] out of memory

Fix is the same as #7744

@davidsaada

Pull request type

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

[davidsaada]

LGTM.

[geky]

Thanks for this!

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3411
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8484/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 3038
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8484/

[mbed-ci]

Test : SUCCESS

Build number : 3208
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8484/3208