Remove mendersoftware/scopestack and mendersoftware/log dependencies

Client code uses two internal dependencies to nicely print logs and errors: mendersoftware/log and mendersoftware/scopestack. These are not working as intended originally and are creating maintainability problems, specifically with the official Debian packages.

One recent problem was for stopestack failing to build from source with golang 1.13 [1] and mender-client package therefore being marked for autoremoval from Debian repositories.

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=952188

Hence, we would like to remove these dependencies for the Mender client.

Acceptance criteria:

• All these dependencies removed from client:
  • github.com/mendersoftware/log
  • github.com/mendersoftware/scopestack
• mender -log-modules argument deprecated with a warning (but not removed, needs to be backwards compatible)