This PR adds retry logic to the process of cloning a git repository.
Currently, it retries only if the output of the git clone command
contains the string `Connection reset`.
Probably, there are more cases where retry is reasonable, but I'm not
sure what they are.
The number of retries is hardcoded to 10 with increasing delay between
retries — in the same way as it is done in #4265, which served me as an
example.
The initial use case is described in #4724.