threads test: increase threads heap size
threads test: increase threads heap size

ryankurte/mbed-os,mbedmicro/mbed,andcor02/mbed-os,karsev/mbed-os,CalSol/mbed,andcor02/mbed-os,betzw/mbed-os,CalSol/mbed,betzw/mbed-os,ryankurte/mbed-os,mazimkhan/mbed-os,mbedmicro/mbed,mazimkhan/mbed-os,karsev/mbed-os,c1728p9/mbed-os,c1728p9/mbed-os,c1728p9/mbed-os,CalSol/mbed,ryankurte/mbed-os,c1728p9/mbed-os,Archcady/mbed-os,c1728p9/mbed-os,mazimkhan/mbed-os,CalSol/mbed,mazimkhan/mbed-os,mbedmicro/mbed,Archcady/mbed-os,kjbracey-arm/mbed,Archcady/mbed-os,karsev/mbed-os,kjbracey-arm/mbed,betzw/mbed-os,CalSol/mbed,andcor02/mbed-os,Archcady/mbed-os,mazimkhan/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,betzw/mbed-os,betzw/mbed-os,andcor02/mbed-os,Archcady/mbed-os,ryankurte/mbed-os,Archcady/mbed-os,karsev/mbed-os,CalSol/mbed,ryankurte/mbed-os,kjbracey-arm/mbed,betzw/mbed-os,ryankurte/mbed-os,mbedmicro/mbed,mbedmicro/mbed,karsev/mbed-os,andcor02/mbed-os,mazimkhan/mbed-os,karsev/mbed-os,andcor02/mbed-os