Implemented TestHost functions:

[rasmus-kirk]

Purpose

See the related issue (#558)

Also see the accompanying PR

Tested using this script, that compiles cargo concordium and runs the unit tests in concordium-std:

CONCORDIUM_STD_PATH="/path/to/concordium-std"
CARGO_CONCORDIUM_PATH="/path/to/cargo-concordium/Cargo.toml"

pushd "$CONCORDIUM_STD_PATH"
cargo run --manifest-path "$CARGO_CONCORDIUM_PATH" -- concordium test --only-unit-tests -- --features internal-wasm-test
popd

Changes

• Implemented the following TestHost functions:
  • set_slot_time
  • get_slot_time
  • set_receive_self_address
  • get_receive_self_address
  • set_receive_self_balance
  • get_receive_self_balance

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[limemloh]

Looks good