Explicit errors on missing parameters

[RomLecat]

Description

When omitting certain parameters, such as region (either from env or conf), the error is not really explicit (it only produces malformed URL).
Packer could return a more explicit error to indicate the missing parameter(s).

Use Case(s)

N/A

Potential configuration

N/A

Potential References

See outscale/omi-packer#3.

[outscale-mdr]

Hello @RomLecat,

Thank you for this idea. We will implement it as soon as possible.

Best regards,
Maxime