hsm: add possibility to update HSM firmware from middleware

[Tomasvrba]

This commit:

• Adds the AvailableHSMVersion Redis key: hsm:firmware:version
• Adds the HSMUpdateAvailable() method to the middleware which compares the version of the running HSM firmware and the AvailableHSMVersion Redis key
• If a new version is available, the main() function executes the update via the hsm immediately after the middleware is started
• The signed firmware file is assumed to be in /opt/shift/hsm/firmware-bitboxbase.signed.bin which is the default value of the hsmFirmwareFile flag
• Together with the updateHSMFirmware, this can be used to force flash firmware from a custom location
• If an update is successful, reboot back into the firmware via the middleware so that the middleware has access to the new hsmFirmware

[Tomasvrba]

@Stadicus We will also need to set the AvailableHSMVersion Redis key on build. I'll leave that to you?

[Tomasvrba]

@benma Could you please take another quick look over my changes which address your review?