more resilient subsystems (#1908)

* backing: extract log target

* bitfield-signing: extract log target

* utils: fix a typo

* provisioner: extract log target

* candidate selection: remove unused error variant

* bitfield-distribution: change the return type of run

* pov-distribution: extract log target

* collator-protocol: simplify runtime request

* collation-generation: do not exit early on error

* collation-generation: do not exit on double init

* collator-protocol: do not exit on errors and rename LOG_TARGET

* collator-protocol: a workaround for ununused imports warning

* Update node/network/bitfield-distribution/src/lib.rs

* collation-generation: elevate warn! to error!

* collator-protocol: fix imports

* post merge fix

* fix compilation

polkadot/node/core/backing/src/lib.rs

@@ -68,6 +68,8 @@ use statement_table::{
 };
 use thiserror::Error;
 
+const LOG_TARGET: &str = "candidate_backing";
+
 #[derive(Debug, Error)]
 enum Error {
 	#[error("Candidate is not found")]
@@ -763,7 +765,7 @@ impl util::JobTrait for CandidateBackingJob {
 						Ok(x) => x,
 						Err(e) => {
 							log::warn!(
-								target: "candidate_backing",
+								target: LOG_TARGET,
 								"Failed to fetch runtime API data for job: {:?}",
 								e,
 							);
@@ -803,7 +805,7 @@ impl util::JobTrait for CandidateBackingJob {
 				Err(util::Error::NotAValidator) => { return Ok(()) },
 				Err(e) => {
 					log::warn!(
-						target: "candidate_backing",
+						target: LOG_TARGET,
 						"Cannot participate in candidate backing: {:?}",
 						e
 					);