Fix gulp methods for targeting arm systems

[ted-piotrowski]

prepareDebPackage/buildDepPackage are passed the architecture string "armhf". They use this string to index into an object inside

function getDebPackageArch(arch) {
    return { x64: 'amd64', ia32: 'i386', arm: 'armhf' }[arch];
}

However, the object key is "arm" not "armhf", causing the function to return 'undefined' which results in a broken package. Same applies for the Rpm equivalent.

Bug was introduced in the original change:
007c2ca

[msftclas]

Hi @ted-piotrowski, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. Real humans will now evaluate your PR.

TTYL, MSBOT;

[coveralls]

Coverage remained the same at 61.19% when pulling 98c1902 on ted-piotrowski:master into 7baf009 on Microsoft:master.

[Tyriar]

👍 thanks!