BFT Block Puller: unit test the DeliveryRequester

[tock-ibm]

add unit tests for the
internal/pkg/peer/blocksprovider/delivery_requester.go
against a real GRPC service, with security etc.

[solo-daemon]

@tock-ibm I would like to work on this. Is someone working on this?

[solo-daemon]

Also it seems that the file may have been moved to common/deliverclient/blocksprovider/delivery_requester.go

[tock-ibm]

@solo-daemon Thanks for the contribution! I merged your unit tests PR, but see comments here:
#4798 (comment)

If you could address these comments in a new PR that would be great.

[solo-daemon]

@tock-ibm sure I would add another pr shortly.

[solo-daemon]

@tock-ibm I have added the suggested changes please take a look