Remove redundant graph execution exception logging

[TimurKasatkin]

No description provided.

[TimurKasatkin]

Such logging has following drawbacks:

1. it produces message "kotlin.Unit" since empty message lambda provided
2. What is the motivation of such logging if we call executionResultFuture.completeExceptionally? By doing so library clients loose ability to decide how to handle occurred exception - it is always logged even if graph future still failed with exception. In practice, with this logging error message is duplicated by this logger and client app's logger.

[swarmshine]

• There was several cases, when application level logging was incorrectly setup. Presence of logger on completable-reactor level helped resolve issues: it provided detailed stack trace information that app level logging missed.
• By removing this library level logging you making decision on behalf of the the user of application that he should take care of logging in particular way. We removing option: what if number of such errors is small, and user can simply decide do not overwhelm app logic with logging and benefit of the option that completable-reactor itself will provide reasonable diagnostic information if something happens.
• There are another project: bank131 that actively uses reactor. And seems like there are no problems there with this logging. Maybe better option would be to provide dedicated logger name and in user project simply disable particular log via logging option. E.g.
  here we can change logger name to ru.fix.completable.reactor.user.exception
  And in application we can add option: log4j ru.fix.completable.reactor.user.exception = OFF

[swarmshine]

• There was several cases, when application level logging was incorrectly setup. Presence of logger on completable-reactor level helped resolve issues: it provided detailed stack trace information that app level logging missed.
• By removing this library level logging you making decision on behalf of the the user of application that he should take care of logging in particular way. We removing option: what if number of such errors is small, and user can simply decide do not overwhelm app logic with logging and benefit of the option that completable-reactor itself will provide reasonable diagnostic information if something happens.
• There are another project: bank131 that actively uses reactor. And seems like there are no problems there with this logging. Maybe better option would be to provide dedicated logger name and in user project simply disable particular log via logging option. E.g.
  here we can change logger name to ru.fix.completable.reactor.user.exception
  And in application we can add option: log4j ru.fix.completable.reactor.user.exception = OFF