Add support to update modules

[joelguittet]

The purpose of this Pull Request is to add support to update modules (#40)

No examples are available at the moment. To use modules, the module type should be registered to the mender client just after mender_cleint_init is called, as shown on the following skeleton:

/* Register module-readme artifact type */
if (MENDER_OK != mender_client_register_artifact_type("hello-world", &module_hello_world_cb, false, NULL)) {
    mender_log_error("Unable to register 'module-readme' artifact type");
    ret = EXIT_FAILURE;
    goto RELEASE;
}

The callback is used to retrieve module content when a deployment is in progress. Because this mechanism is generic, the mender client doesn't provide much more support and specific application implementation should be done depending of the module.

static mender_err_t
module_hello_world_cb(char *id, char *artifact_name, char *type, cJSON *meta_data, char *filename, size_t size, void *data, size_t index, size_t length) {
    //specific stuff depending of the module, upgrading local files or an external module for example
    return MENDER_OK; //Or MENDER_FAIL in case of error, to abord the download
}

Multiple modules types can be registered. Support of artifact name verification after reboot is also provided to report success/failure after installation (latest argument of the mender_client_register_artifact_type function).

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
27 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud