Improve error message about command not
Improve error message about command not

being valid. Hint that it could be a valid command in the other mode
(asm/arm).

MikhailTryakhov/azure-xplat-cli,amarzavery/azure-xplat-cli,huangpf/azure-xplat-cli,amarzavery/azure-xplat-cli,ClogenyTechnologies/azure-xplat-cli,AzureRT/azure-xplat-cli,ClogenyTechnologies/azure-xplat-cli,MikhailTryakhov/azure-xplat-cli,amarzavery/azure-xplat-cli,wastoresh/azure-xplat-cli,yugangw-msft/azure-sdk-tools-xplat,huangpf/azure-xplat-cli,AzureRT/azure-xplat-cli,yugangw-msft/azure-sdk-tools-xplat,wastoresh/azure-xplat-cli,huangpf/azure-xplat-cli,yugangw-msft/azure-xplat-cli,yugangw-msft/azure-sdk-tools-xplat,yugangw-msft/azure-xplat-cli,amarzavery/azure-xplat-cli,MikhailTryakhov/azure-xplat-cli,Azure/azure-xplat-cli,yugangw-msft/azure-xplat-cli,xingwu1/azure-xplat-cli,yugangw-msft/azure-xplat-cli,MsysTechnologiesllc/azure-xplat-cli,Azure/azure-xplat-cli,MsysTechnologiesllc/azure-xplat-cli,xingwu1/azure-xplat-cli,yugangw-msft/azure-xplat-cli,amarzavery/azure-xplat-cli,Azure/azure-xplat-cli,AzureRT/azure-xplat-cli,wastoresh/azure-xplat-cli,MsysTechnologiesllc/azure-xplat-cli,Azure/azure-xplat-cli,ClogenyTechnologies/azure-xplat-cli,Azure/azure-xplat-cli,xingwu1/azure-xplat-cli